Index: src/OFKernelEventObserver_epoll.m
==================================================================
--- src/OFKernelEventObserver_epoll.m
+++ src/OFKernelEventObserver_epoll.m
@@ -49,16 +49,18 @@
 	@try {
 		struct epoll_event event;
 
 #ifdef HAVE_EPOLL_CREATE1
 		if ((_epfd = epoll_create1(EPOLL_CLOEXEC)) == -1)
-			@throw [OFInitializationFailedException exception];
+			@throw [OFInitializationFailedException
+			    exceptionWithClass: [self class]];
 #else
 		int flags;
 
 		if ((_epfd = epoll_create(1)) == -1)
-			@throw [OFInitializationFailedException exception];
+			@throw [OFInitializationFailedException
+			    exceptionWithClass: [self class]];
 
 		if ((flags = fcntl(_epfd, F_GETFD, 0)) != -1)
 			fcntl(_epfd, F_SETFD, flags | FD_CLOEXEC);
 #endif
 
@@ -69,11 +71,12 @@
 		memset(&event, 0, sizeof(event));
 		event.events = EPOLLIN;
 		event.data.ptr = [OFNull null];
 
 		if (epoll_ctl(_epfd, EPOLL_CTL_ADD, _cancelFD[0], &event) == -1)
-			@throw [OFInitializationFailedException exception];
+			@throw [OFInitializationFailedException
+			    exceptionWithClass: [self class]];
 	} @catch (id e) {
 		[self release];
 		@throw e;
 	}
 

Index: src/OFKernelEventObserver_select.m
==================================================================
--- src/OFKernelEventObserver_select.m
+++ src/OFKernelEventObserver_select.m
@@ -47,11 +47,12 @@
 {
 	self = [super init];
 
 #ifndef OF_WINDOWS
 	if (_cancelFD[0] >= (int)FD_SETSIZE)
-		@throw [OFInitializationFailedException exception];
+		@throw [OFInitializationFailedException
+		    exceptionWithClass: [self class]];
 #endif
 
 	FD_ZERO(&_readFDs);
 	FD_ZERO(&_writeFDs);
 	FD_SET(_cancelFD[0], &_readFDs);

Index: src/OFString.m
==================================================================
--- src/OFString.m
+++ src/OFString.m
@@ -588,11 +588,12 @@
 
 	placeholder.isa = [OFString_placeholder class];
 
 #if defined(HAVE_STRTOF_L) || defined(HAVE_STRTOD_L)
 	if ((cLocale = newlocale(LC_ALL_MASK, "C", NULL)) == NULL)
-		@throw [OFInitializationFailedException exception];
+		@throw [OFInitializationFailedException
+		    exceptionWithClass: self];
 #endif
 }
 
 + alloc
 {

Index: src/exceptions/OFAcceptFailedException.h
==================================================================
--- src/exceptions/OFAcceptFailedException.h
+++ src/exceptions/OFAcceptFailedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_SOCKETS
 # error No sockets available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFAcceptFailedException \
  *	  OFAcceptFailedException.h ObjFW/OFAcceptFailedException.h
  *
  * @brief An exception indicating that accepting a connection failed.
@@ -60,5 +62,7 @@
  * @return An initialized accept failed exception
  */
 - initWithSocket: (id)socket
 	   errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFAddressTranslationFailedException.h
==================================================================
--- src/exceptions/OFAddressTranslationFailedException.h
+++ src/exceptions/OFAddressTranslationFailedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_SOCKETS
 # error No sockets available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFAddressTranslationFailedException \
  *	  OFAddressTranslationFailedException.h \
  *	  ObjFW/OFAddressTranslationFailedException.h
  *
@@ -34,31 +36,33 @@
 }
 
 /*!
  * The host for which the address translation was requested.
  */
-@property (readonly, nonatomic) OFString *host;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) OFString *host;
 
 /*!
  * @brief Creates a new, autoreleased address translation failed exception.
  *
  * @param host The host for which translation was requested
  * @return A new, autoreleased address translation failed exception
  */
-+ (instancetype)exceptionWithHost: (OFString*)host;
++ (instancetype)exceptionWithHost: (nullable OFString*)host;
 
-+ (instancetype)exceptionWithHost: (OFString*)host
++ (instancetype)exceptionWithHost: (nullable OFString*)host
 			    error: (int)error;
 + (instancetype)exceptionWithError: (int)error;
 
 /*!
  * @brief Initializes an already allocated address translation failed exception.
  *
  * @param host The host for which translation was requested
  * @return An initialized address translation failed exception
  */
-- initWithHost: (OFString*)host;
+- initWithHost: (nullable OFString*)host;
 
-- (instancetype)initWithHost: (OFString*)host
+- (instancetype)initWithHost: (nullable OFString*)host
 		       error: (int)error;
 - (instancetype)initWithError: (int)error;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFAddressTranslationFailedException.m
==================================================================
--- src/exceptions/OFAddressTranslationFailedException.m
+++ src/exceptions/OFAddressTranslationFailedException.m
@@ -39,11 +39,12 @@
 {
 	if (self != [OFAddressTranslationFailedException class])
 		return;
 
 	if (!of_mutex_new(&mutex))
-		@throw [OFInitializationFailedException exception];
+		@throw [OFInitializationFailedException
+		    exceptionWithClass: class];
 }
 #endif
 
 + (instancetype)exceptionWithHost: (OFString*)host
 {

Index: src/exceptions/OFAllocFailedException.h
==================================================================
--- src/exceptions/OFAllocFailedException.h
+++ src/exceptions/OFAllocFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFObject.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFString;
 
 /*!
  * @class OFAllocFailedException \
  *	  OFAllocFailedException.h ObjFW/OFAllocFailedException.h
@@ -39,5 +41,7 @@
  *
  * @return A description of the exception
  */
 - (OFString*)description;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFAlreadyConnectedException.h
==================================================================
--- src/exceptions/OFAlreadyConnectedException.h
+++ src/exceptions/OFAlreadyConnectedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_SOCKETS
 # error No sockets available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFAlreadyConnectedException \
  *	  OFAlreadyConnectedException.h ObjFW/OFAlreadyConnectedException.h
  *
  * @brief An exception indicating an attempt to connect or bind an already
@@ -33,23 +35,25 @@
 }
 
 /*!
  * The socket which is already connected.
  */
-@property (readonly, nonatomic) id socket;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) id socket;
 
 /*!
  * @brief Creates a new, autoreleased already connected exception.
  *
  * @param socket The socket which is already connected
  * @return A new, autoreleased already connected exception
  */
-+ (instancetype)exceptionWithSocket: (id)socket;
++ (instancetype)exceptionWithSocket: (nullable id)socket;
 
 /*!
  * @brief Initializes an already allocated already connected exception.
  *
  * @param socket The socket which is already connected
  * @return An initialized already connected exception
  */
-- initWithSocket: (id)socket;
+- initWithSocket: (nullable id)socket;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFBindFailedException.h
==================================================================
--- src/exceptions/OFBindFailedException.h
+++ src/exceptions/OFBindFailedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_SOCKETS
 # error No sockets available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFBindFailedException \
  *	  OFBindFailedException.h ObjFW/OFBindFailedException.h
  *
  * @brief An exception indicating that binding a socket failed.
@@ -80,5 +82,7 @@
 - initWithHost: (OFString*)host
 	  port: (uint16_t)port
 	socket: (id)socket
 	 errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFChangeCurrentDirectoryPathFailedException.h
==================================================================
--- src/exceptions/OFChangeCurrentDirectoryPathFailedException.h
+++ src/exceptions/OFChangeCurrentDirectoryPathFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFChangeCurrentDirectoryPathFailedException \
  *	  OFChangeCurrentDirectoryPathFailedException.h \
  *	  ObjFW/OFChangeCurrentDirectoryPathFailedException.h
  *
@@ -61,5 +63,7 @@
  * @return An initialized change current directory path failed exception
  */
 - initWithPath: (OFString*)path
 	 errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFChangeOwnerFailedException.h
==================================================================
--- src/exceptions/OFChangeOwnerFailedException.h
+++ src/exceptions/OFChangeOwnerFailedException.h
@@ -14,11 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
-#ifdef OF_HAVE_CHOWN
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFChangeOwnerFailedException \
  *	  OFChangeOwnerFailedException.h ObjFW/OFChangeOwnerFailedException.h
  *
  * @brief An exception indicating that changing the owner of an item failed.
@@ -35,16 +36,16 @@
 @property (readonly, nonatomic) OFString *path;
 
 /*!
  * The new owner for the item.
  */
-@property (readonly, nonatomic) OFString *owner;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) OFString *owner;
 
 /*!
  * The new group for the item.
  */
-@property (readonly, nonatomic) OFString *group;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) OFString *group;
 
 /*!
  * The errno of the error that occurred.
  */
 @property (readonly) int errNo;
@@ -57,12 +58,12 @@
  * @param group The new group for the item
  * @param errNo The errno of the error that occurred
  * @return A new, autoreleased change owner failed exception
  */
 + (instancetype)exceptionWithPath: (OFString*)path
-			    owner: (OFString*)owner
-			    group: (OFString*)group
+			    owner: (nullable OFString*)owner
+			    group: (nullable OFString*)group
 			    errNo: (int)errNo;
 
 /*!
  * @brief Initializes an already allocated change owner failed exception.
  *
@@ -71,10 +72,11 @@
  * @param group The new group for the item
  * @param errNo The errno of the error that occurred
  * @return An initialized change owner failed exception
  */
 - initWithPath: (OFString*)path
-	 owner: (OFString*)owner
-	 group: (OFString*)group
+	 owner: (nullable OFString*)owner
+	 group: (nullable OFString*)group
 	 errNo: (int)errNo;
 @end
-#endif
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFChangeOwnerFailedException.m
==================================================================
--- src/exceptions/OFChangeOwnerFailedException.m
+++ src/exceptions/OFChangeOwnerFailedException.m
@@ -17,11 +17,10 @@
 #include "config.h"
 
 #import "OFChangeOwnerFailedException.h"
 #import "OFString.h"
 
-#ifdef OF_HAVE_CHOWN
 @implementation OFChangeOwnerFailedException
 @synthesize path = _path, owner = _owner, group = _group, errNo = _errNo;
 
 + (instancetype)exceptionWithPath: (OFString*)path
 			    owner: (OFString*)owner
@@ -82,6 +81,5 @@
 		return [OFString stringWithFormat:
 		    @"Failed to change owner of item at path %@ to %@:%@: %@",
 		    _path, _owner, _group, of_strerror(_errNo)];
 }
 @end
-#endif

Index: src/exceptions/OFChangePermissionsFailedException.h
==================================================================
--- src/exceptions/OFChangePermissionsFailedException.h
+++ src/exceptions/OFChangePermissionsFailedException.h
@@ -16,10 +16,12 @@
 
 #include <sys/types.h>
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFChangePermissionsFailedException \
  *	  OFChangePermissionsFailedException.h \
  *	  ObjFW/OFChangePermissionsFailedException.h
  *
@@ -70,5 +72,7 @@
  */
 - initWithPath: (OFString*)path
    permissions: (mode_t)permissions
 	 errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFChecksumFailedException.h
==================================================================
--- src/exceptions/OFChecksumFailedException.h
+++ src/exceptions/OFChecksumFailedException.h
@@ -14,13 +14,17 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFChecksumFailedException \
  *	  OFChecksumFailedException.h ObjFW/OFChecksumFailedException.h
  *
  * @brief An exception indicating that a checksum did not match.
  */
 @interface OFChecksumFailedException: OFException
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFConditionBroadcastFailedException.h
==================================================================
--- src/exceptions/OFConditionBroadcastFailedException.h
+++ src/exceptions/OFConditionBroadcastFailedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_THREADS
 # error No threads available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFCondition;
 
 /*!
  * @class OFConditionBroadcastFailedException \
  *	  OFConditionBroadcastFailedException.h \
@@ -35,23 +37,25 @@
 }
 
 /*!
  * The condition which could not be broadcasted.
  */
-@property (readonly, nonatomic) OFCondition *condition;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) OFCondition *condition;
 
 /*!
  * @brief Returns a new, autoreleased condition broadcast failed exception.
  *
  * @param condition The condition which could not be broadcasted
  * @return A new, autoreleased condition broadcast failed exception
  */
-+ (instancetype)exceptionWithCondition: (OFCondition*)condition;
++ (instancetype)exceptionWithCondition: (nullable OFCondition*)condition;
 
 /*!
  * @brief Initializes an already allocated condition broadcast failed exception.
  *
  * @param condition The condition which could not be broadcasted
  * @return An initialized condition broadcast failed exception
  */
-- initWithCondition: (OFCondition*)condition;
+- initWithCondition: (nullable OFCondition*)condition;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFConditionBroadcastFailedException.m
==================================================================
--- src/exceptions/OFConditionBroadcastFailedException.m
+++ src/exceptions/OFConditionBroadcastFailedException.m
@@ -26,15 +26,10 @@
 + (instancetype)exceptionWithCondition: (OFCondition*)condition
 {
 	return [[[self alloc] initWithCondition: condition] autorelease];
 }
 
-- init
-{
-	OF_INVALID_INIT_METHOD
-}
-
 - initWithCondition: (OFCondition*)condition
 {
 	self = [super init];
 
 	_condition = [condition retain];
@@ -49,9 +44,13 @@
 	[super dealloc];
 }
 
 - (OFString*)description
 {
-	return [OFString stringWithFormat:
-	    @"Broadcasting a condition of type %@ failed!", [_condition class]];
+	if (_condition != nil)
+		return [OFString stringWithFormat:
+		    @"Broadcasting a condition of type %@ failed!",
+		    [_condition class]];
+	else
+		return @"Broadcasting a condition failed!";
 }
 @end

Index: src/exceptions/OFConditionSignalFailedException.h
==================================================================
--- src/exceptions/OFConditionSignalFailedException.h
+++ src/exceptions/OFConditionSignalFailedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_THREADS
 # error No threads available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFCondition;
 
 /*!
  * @class OFConditionSignalFailedException \
  *	  OFConditionSignalFailedException.h \
@@ -35,23 +37,25 @@
 }
 
 /*!
  * The condition which could not be signaled.
  */
-@property (readonly, nonatomic) OFCondition *condition;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) OFCondition *condition;
 
 /*!
  * @brief Creates a new, autoreleased condition signal failed exception.
  *
  * @param condition The condition which could not be signaled
  * @return A new, autoreleased condition signal failed exception
  */
-+ (instancetype)exceptionWithCondition: (OFCondition*)condition;
++ (instancetype)exceptionWithCondition: (nullable OFCondition*)condition;
 
 /*!
  * @brief Initializes an already allocated condition signal failed exception.
  *
  * @param condition The condition which could not be signaled
  * @return An initialized condition signal failed exception
  */
-- initWithCondition: (OFCondition*)condition;
+- initWithCondition: (nullable OFCondition*)condition;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFConditionSignalFailedException.m
==================================================================
--- src/exceptions/OFConditionSignalFailedException.m
+++ src/exceptions/OFConditionSignalFailedException.m
@@ -26,15 +26,10 @@
 + (instancetype)exceptionWithCondition: (OFCondition*)condition
 {
 	return [[[self alloc] initWithCondition: condition] autorelease];
 }
 
-- init
-{
-	OF_INVALID_INIT_METHOD
-}
-
 - initWithCondition: (OFCondition*)condition
 {
 	self = [super init];
 
 	_condition = [condition retain];
@@ -49,9 +44,13 @@
 	[super dealloc];
 }
 
 - (OFString*)description
 {
-	return [OFString stringWithFormat:
-	    @"Signaling a condition of type %@ failed!", [_condition class]];
+	if (_condition != nil)
+		return [OFString stringWithFormat:
+		    @"Signaling a condition of type %@ failed!",
+		    [_condition class]];
+	else
+		return @"Signaling a condition failed!";
 }
 @end

Index: src/exceptions/OFConditionStillWaitingException.h
==================================================================
--- src/exceptions/OFConditionStillWaitingException.h
+++ src/exceptions/OFConditionStillWaitingException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_THREADS
 # error No threads available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFCondition;
 
 /*!
  * @class OFConditionStillWaitingException \
  *	  OFConditionStillWaitingException.h \
@@ -36,23 +38,25 @@
 }
 
 /*!
  * The condition for which is still being waited.
  */
-@property (readonly, nonatomic) OFCondition *condition;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) OFCondition *condition;
 
 /*!
  * @brief Creates a new, autoreleased condition still waiting exception.
  *
  * @param condition The condition for which is still being waited
  * @return A new, autoreleased condition still waiting exception
  */
-+ (instancetype)exceptionWithCondition: (OFCondition*)condition;
++ (instancetype)exceptionWithCondition: (nullable OFCondition*)condition;
 
 /*!
  * @brief Initializes an already allocated condition still waiting exception.
  *
  * @param condition The condition for which is still being waited
  * @return An initialized condition still waiting exception
  */
-- initWithCondition: (OFCondition*)condition;
+- initWithCondition: (nullable OFCondition*)condition;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFConditionStillWaitingException.m
==================================================================
--- src/exceptions/OFConditionStillWaitingException.m
+++ src/exceptions/OFConditionStillWaitingException.m
@@ -26,15 +26,10 @@
 + (instancetype)exceptionWithCondition: (OFCondition*)condition
 {
 	return [[[self alloc] initWithCondition: condition] autorelease];
 }
 
-- init
-{
-	OF_INVALID_INIT_METHOD
-}
-
 - initWithCondition: (OFCondition*)condition
 {
 	self = [super init];
 
 	_condition = [condition retain];
@@ -49,10 +44,15 @@
 	[super dealloc];
 }
 
 - (OFString*)description
 {
-	return [OFString stringWithFormat:
-	    @"Deallocation of a condition of type %@ was tried, even though a "
-	    @"thread was still waiting for it!", [_condition class]];
+	if (_condition != nil)
+		return [OFString stringWithFormat:
+		    @"Deallocation of a condition of type %@ was tried, even "
+		    "though a thread was still waiting for it!",
+		    [_condition class]];
+	else
+		return @"Deallocation of a condition was tried, even though a "
+		    "thread was still waiting for it!";
 }
 @end

Index: src/exceptions/OFConditionWaitFailedException.h
==================================================================
--- src/exceptions/OFConditionWaitFailedException.h
+++ src/exceptions/OFConditionWaitFailedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_THREADS
 # error No threads available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFCondition;
 
 /*!
  * @class OFConditionWaitFailedException \
  *	  OFConditionWaitFailedException.h \
@@ -35,23 +37,25 @@
 }
 
 /*!
  * The condition for which could not be waited.
  */
-@property (readonly, nonatomic) OFCondition *condition;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) OFCondition *condition;
 
 /*!
  * @brief Creates a new, autoreleased condition wait failed exception.
  *
  * @param condition The condition for which could not be waited
  * @return A new, autoreleased condition wait failed exception
  */
-+ (instancetype)exceptionWithCondition: (OFCondition*)condition;
++ (instancetype)exceptionWithCondition: (nullable OFCondition*)condition;
 
 /*!
  * @brief Initializes an already allocated condition wait failed exception.
  *
  * @param condition The condition for which could not be waited
  * @return An initialized condition wait failed exception
  */
-- initWithCondition: (OFCondition*)condition;
+- initWithCondition: (nullable OFCondition*)condition;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFConditionWaitFailedException.m
==================================================================
--- src/exceptions/OFConditionWaitFailedException.m
+++ src/exceptions/OFConditionWaitFailedException.m
@@ -26,15 +26,10 @@
 + (instancetype)exceptionWithCondition: (OFCondition*)condition
 {
 	return [[[self alloc] initWithCondition: condition] autorelease];
 }
 
-- init
-{
-	OF_INVALID_INIT_METHOD
-}
-
 - initWithCondition: (OFCondition*)condition
 {
 	self = [super init];
 
 	_condition = [condition retain];
@@ -49,9 +44,13 @@
 	[super dealloc];
 }
 
 - (OFString*)description
 {
-	return [OFString stringWithFormat:
-	    @"Waiting for a condition of type %@ failed!", [_condition class]];
+	if (_condition != nil)
+		return [OFString stringWithFormat:
+		    @"Waiting for a condition of type %@ failed!",
+		    [_condition class]];
+	else
+		return @"Waiting for a condition failed!";
 }
 @end

Index: src/exceptions/OFConnectionFailedException.h
==================================================================
--- src/exceptions/OFConnectionFailedException.h
+++ src/exceptions/OFConnectionFailedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_SOCKETS
 # error No sockets available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFConnectionFailedException \
  *	  OFConnectionFailedException.h ObjFW/OFConnectionFailedException.h
  *
  * @brief An exception indicating that a connection could not be established.
@@ -104,5 +106,7 @@
 - initWithHost: (OFString*)host
 	  port: (uint16_t)port
 	socket: (id)socket
 	 errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFCopyItemFailedException.h
==================================================================
--- src/exceptions/OFCopyItemFailedException.h
+++ src/exceptions/OFCopyItemFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFCopyItemFailedException \
  *	  OFCopyItemFailedException.h ObjFW/OFCopyItemFailedException.h
  *
  * @brief An exception indicating that copying a item failed.
@@ -65,5 +67,7 @@
  */
 - initWithSourcePath: (OFString*)sourcePath
      destinationPath: (OFString*)destinationPath
 	       errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFCreateDirectoryFailedException.h
==================================================================
--- src/exceptions/OFCreateDirectoryFailedException.h
+++ src/exceptions/OFCreateDirectoryFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFCreateDirectoryFailedException \
  *	  OFCreateDirectoryFailedException.h \
  *	  ObjFW/OFCreateDirectoryFailedException.h
  *
@@ -59,5 +61,7 @@
  * @return An initialized create directory failed exception
  */
 - initWithPath: (OFString*)path
 	 errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFCreateSymbolicLinkFailedException.h
==================================================================
--- src/exceptions/OFCreateSymbolicLinkFailedException.h
+++ src/exceptions/OFCreateSymbolicLinkFailedException.h
@@ -14,11 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
-#if defined(OF_HAVE_SYMLINK) || defined(OF_WINDOWS)
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFCreateSymbolicLinkFailedException \
  *	  OFCreateSymbolicLinkFailedException.h \
  *	  ObjFW/OFCreateSymbolicLinkFailedException.h
  *
@@ -89,6 +90,7 @@
  */
 - initWithSourcePath: (OFString*)sourcePath
      destinationPath: (OFString*)destinationPath
 	       errNo: (int)errNo;
 @end
-#endif
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFCreateSymbolicLinkFailedException.m
==================================================================
--- src/exceptions/OFCreateSymbolicLinkFailedException.m
+++ src/exceptions/OFCreateSymbolicLinkFailedException.m
@@ -17,11 +17,10 @@
 #include "config.h"
 
 #import "OFCreateSymbolicLinkFailedException.h"
 #import "OFString.h"
 
-#if defined(OF_HAVE_SYMLINK) || defined(OF_WINDOWS)
 @implementation OFCreateSymbolicLinkFailedException
 @synthesize sourcePath = _sourcePath, destinationPath = _destinationPath;
 @synthesize errNo = _errNo;
 
 + (instancetype)exceptionWithSourcePath: (OFString*)sourcePath
@@ -98,6 +97,5 @@
 		return [OFString stringWithFormat:
 		    @"Failed to create symbolic link %@ with destination %@!",
 		    _destinationPath, _sourcePath];
 }
 @end
-#endif

Index: src/exceptions/OFEnumerationMutationException.h
==================================================================
--- src/exceptions/OFEnumerationMutationException.h
+++ src/exceptions/OFEnumerationMutationException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFEnumerationMutationException \
  *	  OFEnumerationMutationException.h \
  *	  ObjFW/OFEnumerationMutationException.h
  *
@@ -48,5 +50,7 @@
  * @param object The object which was mutated during enumeration
  * @return An initialized enumeration mutation exception
  */
 - initWithObject: (id)object;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFException.h
==================================================================
--- src/exceptions/OFException.h
+++ src/exceptions/OFException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFObject.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFString;
 #ifndef DOXYGEN
 @class OFArray OF_GENERIC(ObjectType);
 @class OFMutableArray OF_GENERIC(ObjectType);
 #endif
@@ -164,15 +166,17 @@
  * @brief Returns a backtrace of when the exception was created or nil if no
  *	  backtrace is available.
  *
  * @return A backtrace of when the exception was created
  */
-- (OFArray*)backtrace;
+- (nullable OFArray*)backtrace;
 @end
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 extern OFString* of_strerror(int errNo);
 #ifdef __cplusplus
 }
 #endif
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFGetOptionFailedException.h
==================================================================
--- src/exceptions/OFGetOptionFailedException.h
+++ src/exceptions/OFGetOptionFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFStream;
 
 /*!
  * @class OFGetOptionFailedException \
  *	  OFGetOptionFailedException.h ObjFW/OFGetOptionFailedException.h
@@ -58,5 +60,7 @@
  * @return An initialized get option failed exception
  */
 - initWithStream: (OFStream*)stream
 	   errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFHTTPRequestFailedException.h
==================================================================
--- src/exceptions/OFHTTPRequestFailedException.h
+++ src/exceptions/OFHTTPRequestFailedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_SOCKETS
 # error No sockets available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFHTTPRequest;
 @class OFHTTPResponse;
 
 /*!
  * @class OFHTTPRequestFailedException \
@@ -64,5 +66,7 @@
  * @return A new HTTP request failed exception
  */
 - initWithRequest: (OFHTTPRequest*)request
 	 response: (OFHTTPResponse*)response;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFHashAlreadyCalculatedException.h
==================================================================
--- src/exceptions/OFHashAlreadyCalculatedException.h
+++ src/exceptions/OFHashAlreadyCalculatedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFHashAlreadyCalculatedException \
  *	  OFHashAlreadyCalculatedException.h \
  *	  ObjFW/OFHashAlreadyCalculatedException.h
  *
@@ -47,5 +49,7 @@
  * @param object The hash which has already been calculated
  * @return An initialized hash already calculated exception
  */
 - initWithObject: (id)object;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFInitializationFailedException.h
==================================================================
--- src/exceptions/OFInitializationFailedException.h
+++ src/exceptions/OFInitializationFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFInitializationFailedException \
  *	  OFInitializationFailedException.h \
  *	  ObjFW/OFInitializationFailedException.h
  *
@@ -29,23 +31,25 @@
 }
 
 /*!
  * The class for which initialization failed.
  */
-@property (readonly, nonatomic) Class inClass;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) Class inClass;
 
 /*!
  * @brief Creates a new, autoreleased initialization failed exception.
  *
  * @param class_ The class for which initialization failed
  * @return A new, autoreleased initialization failed exception
  */
-+ (instancetype)exceptionWithClass: (Class)class_;
++ (instancetype)exceptionWithClass: (nullable Class)class_;
 
 /*!
  * @brief Initializes an already allocated initialization failed exception.
  *
  * @param class_ The class for which initialization failed
  * @return An initialized initialization failed exception
  */
-- initWithClass: (Class)class_;
+- initWithClass: (nullable Class)class_;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFInitializationFailedException.m
==================================================================
--- src/exceptions/OFInitializationFailedException.m
+++ src/exceptions/OFInitializationFailedException.m
@@ -25,15 +25,10 @@
 + (instancetype)exceptionWithClass: (Class)class
 {
 	return [[[self alloc] initWithClass: class] autorelease];
 }
 
-- init
-{
-	OF_INVALID_INIT_METHOD
-}
-
 - initWithClass: (Class)class
 {
 	self = [super init];
 
 	_inClass = class;
@@ -41,9 +36,12 @@
 	return self;
 }
 
 - (OFString*)description
 {
-	return [OFString stringWithFormat:
-	    @"Initialization failed for or in class %@!", _inClass];
+	if (_inClass != Nil)
+		return [OFString stringWithFormat:
+		    @"Initialization failed for or in class %@!", _inClass];
+	else
+		return @"Initialization failed!";
 }
 @end

Index: src/exceptions/OFInvalidArgumentException.h
==================================================================
--- src/exceptions/OFInvalidArgumentException.h
+++ src/exceptions/OFInvalidArgumentException.h
@@ -14,13 +14,17 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFInvalidArgumentException \
  *	  OFInvalidArgumentException.h ObjFW/OFInvalidArgumentException.h
  *
  * @brief An exception indicating that the argument is invalid for this method.
  */
 @interface OFInvalidArgumentException: OFException
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFInvalidEncodingException.h
==================================================================
--- src/exceptions/OFInvalidEncodingException.h
+++ src/exceptions/OFInvalidEncodingException.h
@@ -14,13 +14,17 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFInvalidEncodingException \
  *	  OFInvalidEncodingException.h ObjFW/OFInvalidEncodingException.h
  *
  * @brief An exception indicating that the encoding is invalid for this object.
  */
 @interface OFInvalidEncodingException: OFException
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFInvalidFormatException.h
==================================================================
--- src/exceptions/OFInvalidFormatException.h
+++ src/exceptions/OFInvalidFormatException.h
@@ -14,13 +14,17 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFInvalidFormatException \
  *	  OFInvalidFormatException.h ObjFW/OFInvalidFormatException.h
  *
  * @brief An exception indicating that the format is invalid.
  */
 @interface OFInvalidFormatException: OFException
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFInvalidJSONException.h
==================================================================
--- src/exceptions/OFInvalidJSONException.h
+++ src/exceptions/OFInvalidJSONException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFInvalidJSONException \
  *	  OFInvalidJSONException.h ObjFW/OFInvalidJSONException.h
  *
  * @brief An exception indicating a JSON representation is invalid.
@@ -56,5 +58,7 @@
  * @return An initialized invalid JSON exception
  */
 - initWithString: (OFString*)string
 	    line: (size_t)line;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFInvalidServerReplyException.h
==================================================================
--- src/exceptions/OFInvalidServerReplyException.h
+++ src/exceptions/OFInvalidServerReplyException.h
@@ -14,13 +14,17 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFInvalidServerReplyException \
  *	  OFInvalidServerReplyException.h ObjFW/OFInvalidServerReplyException.h
  *
  * @brief An exception indicating that the server sent an invalid reply.
  */
 @interface OFInvalidServerReplyException: OFException
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFLinkFailedException.h
==================================================================
--- src/exceptions/OFLinkFailedException.h
+++ src/exceptions/OFLinkFailedException.h
@@ -14,11 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
-#if defined(OF_HAVE_LINK) || defined(OF_WINDOWS)
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFLinkFailedException \
  *	  OFLinkFailedException.h ObjFW/OFLinkFailedException.h
  *
  * @brief An exception indicating that creating a link failed.
@@ -86,6 +87,7 @@
  */
 - initWithSourcePath: (OFString*)sourcePath
      destinationPath: (OFString*)destinationPath
 	       errNo: (int)errNo;
 @end
-#endif
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFLinkFailedException.m
==================================================================
--- src/exceptions/OFLinkFailedException.m
+++ src/exceptions/OFLinkFailedException.m
@@ -17,11 +17,10 @@
 #include "config.h"
 
 #import "OFLinkFailedException.h"
 #import "OFString.h"
 
-#if defined(OF_HAVE_LINK) || defined(OF_WINDOWS)
 @implementation OFLinkFailedException
 @synthesize sourcePath = _sourcePath, destinationPath = _destinationPath;
 @synthesize errNo = _errNo;
 
 + (instancetype)exceptionWithSourcePath: (OFString*)sourcePath
@@ -97,6 +96,5 @@
 		return [OFString stringWithFormat:
 		    @"Failed to link file %@ to %@!",
 		    _sourcePath, _destinationPath];
 }
 @end
-#endif

Index: src/exceptions/OFListenFailedException.h
==================================================================
--- src/exceptions/OFListenFailedException.h
+++ src/exceptions/OFListenFailedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_SOCKETS
 # error No sockets available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFListenFailedException \
  *	  OFListenFailedException.h ObjFW/OFListenFailedException.h
  *
  * @brief An exception indicating that listening on the socket failed.
@@ -69,5 +71,7 @@
  */
 - initWithSocket: (id)socket
 	 backLog: (int)backLog
 	   errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFLockFailedException.h
==================================================================
--- src/exceptions/OFLockFailedException.h
+++ src/exceptions/OFLockFailedException.h
@@ -15,10 +15,12 @@
  */
 
 #import "OFException.h"
 #import "OFLocking.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFLockFailedException \
  *	  OFLockFailedException.h ObjFW/OFLockFailedException.h
  *
  * @brief An exception indicating that locking a lock failed.
@@ -29,23 +31,25 @@
 }
 
 /*!
  * The lock which could not be locked.
  */
-@property (readonly, nonatomic) id <OFLocking> lock;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) id <OFLocking> lock;
 
 /*!
  * @brief Creates a new, autoreleased lock failed exception.
  *
  * @param lock The lock which could not be locked
  * @return A new, autoreleased lock failed exception
  */
-+ (instancetype)exceptionWithLock: (id <OFLocking>)lock;
++ (instancetype)exceptionWithLock: (nullable id <OFLocking>)lock;
 
 /*!
  * @brief Initializes an already allocated lock failed exception.
  *
  * @param lock The lock which could not be locked
  * @return An initialized lock failed exception
  */
-- initWithLock: (id <OFLocking>)lock;
+- initWithLock: (nullable id <OFLocking>)lock;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFMalformedXMLException.h
==================================================================
--- src/exceptions/OFMalformedXMLException.h
+++ src/exceptions/OFMalformedXMLException.h
@@ -16,10 +16,12 @@
 
 #import "OFException.h"
 
 @class OFXMLParser;
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFMalformedXMLException \
  *	  OFMalformedXMLException.h ObjFW/OFMalformedXMLException.h
  *
  * @brief An exception indicating that a parser encountered malformed XML.
@@ -30,23 +32,25 @@
 }
 
 /*!
  * The parser which encountered malformed XML.
  */
-@property (readonly, nonatomic) OFXMLParser *parser;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) OFXMLParser *parser;
 
 /*!
  * @brief Creates a new, autoreleased malformed XML exception.
  *
  * @param parser The parser which encountered malformed XML
  * @return A new, autoreleased malformed XML exception
  */
-+ (instancetype)exceptionWithParser: (OFXMLParser*)parser;
++ (instancetype)exceptionWithParser: (nullable OFXMLParser*)parser;
 
 /*!
  * @brief Initializes an already allocated malformed XML exception.
  *
  * @param parser The parser which encountered malformed XML
  * @return An initialized malformed XML exception
  */
-- initWithParser: (OFXMLParser*)parser;
+- initWithParser: (nullable OFXMLParser*)parser;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFMemoryNotPartOfObjectException.h
==================================================================
--- src/exceptions/OFMemoryNotPartOfObjectException.h
+++ src/exceptions/OFMemoryNotPartOfObjectException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFMemoryNotPartOfObjectException \
  *	  OFMemoryNotPartOfObjectException.h \
  *	  ObjFW/OFMemoryNotPartOfObjectException.h
  *
@@ -57,5 +59,7 @@
  * @return An initialized memory not part of object exception
  */
 - initWithPointer: (void*)pointer
 	   object: (id)object;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFMoveItemFailedException.h
==================================================================
--- src/exceptions/OFMoveItemFailedException.h
+++ src/exceptions/OFMoveItemFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFMoveItemFailedException \
  *	  OFMoveItemFailedException.h ObjFW/OFMoveItemFailedException.h
  *
  * @brief An exception indicating that moving an item failed.
@@ -65,5 +67,7 @@
  */
 - initWithSourcePath: (OFString*)sourcePath
      destinationPath: (OFString*)destinationPath
 	       errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFNotImplementedException.h
==================================================================
--- src/exceptions/OFNotImplementedException.h
+++ src/exceptions/OFNotImplementedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFNotImplementedException \
  *	  OFNotImplementedException.h ObjFW/OFNotImplementedException.h
  *
  * @brief An exception indicating that a method or part of it is not
@@ -57,5 +59,7 @@
  * @return An initialized not implemented exception
  */
 - initWithSelector: (SEL)selector
 	    object: (id)object;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFNotOpenException.h
==================================================================
--- src/exceptions/OFNotOpenException.h
+++ src/exceptions/OFNotOpenException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFNotOpenException OFNotOpenException.h ObjFW/OFNotOpenException.h
  *
  * @brief An exception indicating an object is not open, connected or bound.
  */
@@ -45,5 +47,7 @@
  * @param object The object which is not open, connected or bound
  * @return An initialized not open exception
  */
 - initWithObject: (id)object;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFObserveFailedException.h
==================================================================
--- src/exceptions/OFObserveFailedException.h
+++ src/exceptions/OFObserveFailedException.h
@@ -13,10 +13,12 @@
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
 #import "OFException.h"
+
+OF_ASSUME_NONNULL_BEGIN
 
 @class OFKernelEventObserver;
 
 /*!
  * @class OFObserveFailedException \
@@ -58,5 +60,7 @@
  * @return An initialized observe failed exception
  */
 - initWithObserver: (OFKernelEventObserver*)observer
 	     errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFOpenItemFailedException.h
==================================================================
--- src/exceptions/OFOpenItemFailedException.h
+++ src/exceptions/OFOpenItemFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFOpenItemFailedException \
  *	  OFOpenItemFailedException.h ObjFW/OFOpenItemFailedException.h
  *
  * @brief An exception indicating an item could not be opened.
@@ -34,11 +36,11 @@
 @property (readonly, nonatomic) OFString *path;
 
 /*!
  * The mode in which the item should have been opened.
  */
-@property (readonly, nonatomic) OFString *mode;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) OFString *mode;
 
 /*!
  * The errno of the error that occurred.
  */
 @property (readonly) int errNo;
@@ -57,11 +59,11 @@
  * @param path A string with the path of the item tried to open
  * @param mode A string with the mode in which the item should have been opened
  * @return A new, autoreleased open item failed exception
  */
 + (instancetype)exceptionWithPath: (OFString*)path
-			     mode: (OFString*)mode;
+			     mode: (nullable OFString*)mode;
 
 /*!
  * @brief Creates a new, autoreleased open item failed exception.
  *
  * @param path A string with the path of the item tried to open
@@ -78,11 +80,11 @@
  * @param mode A string with the mode in which the item should have been opened
  * @param errNo The errno of the error that occurred
  * @return A new, autoreleased open item failed exception
  */
 + (instancetype)exceptionWithPath: (OFString*)path
-			     mode: (OFString*)mode
+			     mode: (nullable OFString*)mode
 			    errNo: (int)errNo;
 
 /*!
  * @brief Initializes an already allocated open item failed exception.
  *
@@ -97,11 +99,11 @@
  * @param path A string with the path of the item which could not be opened
  * @param mode A string with the mode in which the item should have been opened
  * @return An initialized open item failed exception
  */
 - initWithPath: (OFString*)path
-	  mode: (OFString*)mode;
+	  mode: (nullable OFString*)mode;
 
 /*!
  * @brief Initializes an already allocated open item failed exception.
  *
  * @param path A string with the path of the item which could not be opened
@@ -118,8 +120,10 @@
  * @param mode A string with the mode in which the item should have been opened
  * @param errNo The errno of the error that occurred
  * @return An initialized open item failed exception
  */
 - initWithPath: (OFString*)path
-	  mode: (OFString*)mode
+	  mode: (nullable OFString*)mode
 	 errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFOutOfMemoryException.h
==================================================================
--- src/exceptions/OFOutOfMemoryException.h
+++ src/exceptions/OFOutOfMemoryException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFOutOfMemoryException \
  *	  OFOutOfMemoryException.h ObjFW/OFOutOfMemoryException.h
  *
  * @brief An exception indicating there is not enough memory available.
@@ -46,5 +48,7 @@
  * @param requestedSize The size of the memory that could not be allocated
  * @return An initialized no memory exception
  */
 - initWithRequestedSize: (size_t)requestedSize;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFOutOfRangeException.h
==================================================================
--- src/exceptions/OFOutOfRangeException.h
+++ src/exceptions/OFOutOfRangeException.h
@@ -14,13 +14,17 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFOutOfRangeException \
  *	  OFOutOfRangeException.h ObjFW/OFOutOfRangeException.h
  *
  * @brief An exception indicating the given value is out of range.
  */
 @interface OFOutOfRangeException: OFException
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFReadFailedException.h
==================================================================
--- src/exceptions/OFReadFailedException.h
+++ src/exceptions/OFReadFailedException.h
@@ -14,13 +14,17 @@
  * file.
  */
 
 #import "OFReadOrWriteFailedException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFReadFailedException \
  *	  OFReadFailedException.h ObjFW/OFReadFailedException.h
  *
  * @brief An exception indicating that reading from an object failed.
  */
 @interface OFReadFailedException: OFReadOrWriteFailedException
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFReadOrWriteFailedException.h
==================================================================
--- src/exceptions/OFReadOrWriteFailedException.h
+++ src/exceptions/OFReadOrWriteFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFReadOrWriteFailedException \
  *	  OFReadOrWriteFailedException.h ObjFW/OFReadOrWriteFailedException.h
  *
  * @brief An exception indicating that reading from or writing to an object
@@ -91,5 +93,7 @@
  */
 -  initWithObject: (id)object
   requestedLength: (size_t)requestedLength
 	    errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFRemoveItemFailedException.h
==================================================================
--- src/exceptions/OFRemoveItemFailedException.h
+++ src/exceptions/OFRemoveItemFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFRemoveItemFailedException \
  *	  OFRemoveItemFailedException.h ObjFW/OFRemoveItemFailedException.h
  *
  * @brief An exception indicating that removing an item failed.
@@ -56,5 +58,7 @@
  * @return An initialized remove item failed exception
  */
 - initWithPath: (OFString*)path
 	 errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFSandboxActivationFailedException.h
==================================================================
--- src/exceptions/OFSandboxActivationFailedException.h
+++ src/exceptions/OFSandboxActivationFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFSandbox;
 
 /*!
  * @class OFSandboxActivationFailedException \
  *	  OFSandboxActivationFailedException.h \
@@ -59,5 +61,7 @@
  * @return An initialized sandboxing failed exception
  */
 - initWithSandbox: (OFSandbox*)sandbox
 	    errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFSeekFailedException.h
==================================================================
--- src/exceptions/OFSeekFailedException.h
+++ src/exceptions/OFSeekFailedException.h
@@ -15,10 +15,12 @@
  */
 
 #import "OFException.h"
 #import "OFSeekableStream.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFSeekFailedException \
  *	  OFSeekFailedException.h ObjFW/OFSeekFailedException.h
  *
  * @brief An exception indicating that seeking in a stream failed.
@@ -76,5 +78,7 @@
 - initWithStream: (OFSeekableStream*)stream
 	  offset: (of_offset_t)offset
 	  whence: (int)whence
 	   errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFSetOptionFailedException.h
==================================================================
--- src/exceptions/OFSetOptionFailedException.h
+++ src/exceptions/OFSetOptionFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFStream;
 
 /*!
  * @class OFSetOptionFailedException \
  *	  OFSetOptionFailedException.h ObjFW/OFSetOptionFailedException.h
@@ -58,5 +60,7 @@
  * @return An initialized set option failed exception
  */
 - initWithStream: (OFStream*)stream
 	   errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFStatItemFailedException.h
==================================================================
--- src/exceptions/OFStatItemFailedException.h
+++ src/exceptions/OFStatItemFailedException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFStatItemFailedException \
  *	  OFStatItemFailedException.h ObjFW/OFStatItemFailedException.h
  *
  * @brief An exception indicating an item's status could not be retrieved.
@@ -76,5 +78,7 @@
  * @return An initialized stat item failed exception
  */
 - initWithPath: (OFString*)path
 	 errNo: (int)errNo;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFStillLockedException.h
==================================================================
--- src/exceptions/OFStillLockedException.h
+++ src/exceptions/OFStillLockedException.h
@@ -15,10 +15,12 @@
  */
 
 #import "OFException.h"
 #import "OFLocking.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFStillLockedException \
  *	  OFStillLockedException.h ObjFW/OFStillLockedException.h
  *
  * @brief An exception indicating that a lock is still locked.
@@ -29,23 +31,25 @@
 }
 
 /*!
  * The lock which is still locked.
  */
-@property (readonly, nonatomic) id <OFLocking> lock;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) id <OFLocking> lock;
 
 /*!
  * @brief Creates a new, autoreleased still locked exception.
  *
  * @param lock The lock which is still locked
  * @return A new, autoreleased still locked exception
  */
-+ (instancetype)exceptionWithLock: (id <OFLocking>)lock;
++ (instancetype)exceptionWithLock: (nullable id <OFLocking>)lock;
 
 /*!
  * @brief Initializes an already allocated still locked exception.
  *
  * @param lock The lock which is still locked
  * @return An initialized still locked exception
  */
-- initWithLock: (id <OFLocking>)lock;
+- initWithLock: (nullable id <OFLocking>)lock;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFThreadJoinFailedException.h
==================================================================
--- src/exceptions/OFThreadJoinFailedException.h
+++ src/exceptions/OFThreadJoinFailedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_THREADS
 # error No threads available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFThread;
 
 /*!
  * @class OFThreadJoinFailedException \
  *	  OFThreadJoinFailedException.h ObjFW/OFThreadJoinFailedException.h
@@ -34,23 +36,25 @@
 }
 
 /*!
  * The thread which could not be joined.
  */
-@property (readonly, nonatomic) OFThread *thread;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) OFThread *thread;
 
 /*!
  * @brief Creates a new, autoreleased thread join failed exception.
  *
  * @param thread The thread which could not be joined
  * @return A new, autoreleased thread join failed exception
  */
-+ (instancetype)exceptionWithThread: (OFThread*)thread;
++ (instancetype)exceptionWithThread: (nullable OFThread*)thread;
 
 /*!
  * @brief Initializes an already allocated thread join failed exception.
  *
  * @param thread The thread which could not be joined
  * @return An initialized thread join failed exception
  */
-- initWithThread: (OFThread*)thread;
+- initWithThread: (nullable OFThread*)thread;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFThreadJoinFailedException.m
==================================================================
--- src/exceptions/OFThreadJoinFailedException.m
+++ src/exceptions/OFThreadJoinFailedException.m
@@ -26,15 +26,10 @@
 + (instancetype)exceptionWithThread: (OFThread*)thread
 {
 	return [[[self alloc] initWithThread: thread] autorelease];
 }
 
-- init
-{
-	OF_INVALID_INIT_METHOD
-}
-
 - initWithThread: (OFThread*)thread
 {
 	self = [super init];
 
 	_thread = [thread retain];
@@ -49,10 +44,15 @@
 	[super dealloc];
 }
 
 - (OFString*)description
 {
-	return [OFString stringWithFormat:
-	    @"Joining a thread of type %@ failed! Most likely, another thread "
-	    @"already waits for the thread to join.", [_thread class]];
+	if (_thread != nil)
+		return [OFString stringWithFormat:
+		    @"Joining a thread of type %@ failed! Most likely, another "
+		    @"thread already waits for the thread to join.",
+		    [_thread class]];
+	else
+		return @"Joining a thread failed! Most likely, another thread "
+		    @"already waits for the thread to join.";
 }
 @end

Index: src/exceptions/OFThreadStartFailedException.h
==================================================================
--- src/exceptions/OFThreadStartFailedException.h
+++ src/exceptions/OFThreadStartFailedException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_THREADS
 # error No threads available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFThread;
 
 /*!
  * @class OFThreadStartFailedException \
  *	  OFThreadStartFailedException.h ObjFW/OFThreadStartFailedException.h
@@ -34,23 +36,25 @@
 }
 
 /*!
  * The thread which could not be started.
  */
-@property (readonly, nonatomic) OFThread *thread;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) OFThread *thread;
 
 /*!
  * @brief Creates a new, autoreleased thread start failed exception.
  *
  * @param thread The thread which could not be started
  * @return A new, autoreleased thread start failed exception
  */
-+ (instancetype)exceptionWithThread: (OFThread*)thread;
++ (instancetype)exceptionWithThread: (nullable OFThread*)thread;
 
 /*!
  * @brief Initializes an already allocated thread start failed exception.
  *
  * @param thread The thread which could not be started
  * @return An initialized thread start failed exception
  */
-- initWithThread: (OFThread*)thread;
+- initWithThread: (nullable OFThread*)thread;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFThreadStartFailedException.m
==================================================================
--- src/exceptions/OFThreadStartFailedException.m
+++ src/exceptions/OFThreadStartFailedException.m
@@ -26,15 +26,10 @@
 + (instancetype)exceptionWithThread: (OFThread*)thread
 {
 	return [[[self alloc] initWithThread: thread] autorelease];
 }
 
-- init
-{
-	OF_INVALID_INIT_METHOD
-}
-
 - initWithThread: (OFThread*)thread
 {
 	self = [super init];
 
 	_thread = [thread retain];
@@ -49,9 +44,12 @@
 	[super dealloc];
 }
 
 - (OFString*)description
 {
-	return [OFString stringWithFormat:
-	    @"Starting a thread of type %@ failed!", [_thread class]];
+	if (_thread != nil)
+		return [OFString stringWithFormat:
+		    @"Starting a thread of type %@ failed!", [_thread class]];
+	else
+		return @"Starting a thread failed!";
 }
 @end

Index: src/exceptions/OFThreadStillRunningException.h
==================================================================
--- src/exceptions/OFThreadStillRunningException.h
+++ src/exceptions/OFThreadStillRunningException.h
@@ -18,10 +18,12 @@
 
 #ifndef OF_HAVE_THREADS
 # error No threads available!
 #endif
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFThread;
 
 /*!
  * @class OFThreadStillRunningException \
  *	  OFThreadStillRunningException.h ObjFW/OFThreadStillRunningException.h
@@ -34,23 +36,25 @@
 }
 
 /*!
  * The thread which is still running.
  */
-@property (readonly, retain) OFThread *thread;
+@property OF_NULLABLE_PROPERTY (readonly, retain) OFThread *thread;
 
 /*!
  * @brief Creates a new, autoreleased thread still running exception.
  *
  * @param thread The thread which is still running
  * @return A new, autoreleased thread still running exception
  */
-+ (instancetype)exceptionWithThread: (OFThread*)thread;
++ (instancetype)exceptionWithThread: (nullable OFThread*)thread;
 
 /*!
  * @brief Initializes an already allocated thread still running exception.
  *
  * @param thread The thread which is still running
  * @return An initialized thread still running exception
  */
-- initWithThread: (OFThread*)thread;
+- initWithThread: (nullable OFThread*)thread;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFThreadStillRunningException.m
==================================================================
--- src/exceptions/OFThreadStillRunningException.m
+++ src/exceptions/OFThreadStillRunningException.m
@@ -26,15 +26,10 @@
 + (instancetype)exceptionWithThread: (OFThread*)thread
 {
 	return [[[self alloc] initWithThread: thread] autorelease];
 }
 
-- init
-{
-	OF_INVALID_INIT_METHOD
-}
-
 - initWithThread: (OFThread*)thread
 {
 	self = [super init];
 
 	_thread = [thread retain];
@@ -49,10 +44,15 @@
 	[super dealloc];
 }
 
 - (OFString*)description
 {
-	return [OFString stringWithFormat:
-	    @"Deallocation of a thread of type %@ was tried, even though it "
-	    @"was still running!", [_thread class]];
+	if (_thread)
+		return [OFString stringWithFormat:
+		    @"Deallocation of a thread of type %@ was tried, even "
+		    @"though it was still running!",
+		    [_thread class]];
+	else
+		return @"Deallocation of a thread was tried, even though it "
+		    @"was still running!";
 }
 @end

Index: src/exceptions/OFTruncatedDataException.h
==================================================================
--- src/exceptions/OFTruncatedDataException.h
+++ src/exceptions/OFTruncatedDataException.h
@@ -14,14 +14,18 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFTruncatedDataException \
  *	  OFTruncatedDataException.h ObjFW/OFTruncatedDataException.h
  *
  * @brief An exception indicating that data was truncated while it should not
  *	  have been truncated.
  */
 @interface OFTruncatedDataException: OFException
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFUnboundNamespaceException.h
==================================================================
--- src/exceptions/OFUnboundNamespaceException.h
+++ src/exceptions/OFUnboundNamespaceException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFXMLElement;
 
 /*!
  * @class OFUnboundNamespaceException \
  *	  OFUnboundNamespaceException.h ObjFW/OFUnboundNamespaceException.h
@@ -62,5 +64,7 @@
  * @return An initialized unbound namespace exception
  */
 - initWithNamespace: (OFString*)namespace_
 	    element: (OFXMLElement*)element;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFUnboundPrefixException.h
==================================================================
--- src/exceptions/OFUnboundPrefixException.h
+++ src/exceptions/OFUnboundPrefixException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFXMLParser;
 
 /*!
  * @class OFUnboundPrefixException \
  *	  OFUnboundPrefixException.h ObjFW/OFUnboundPrefixException.h
@@ -58,5 +60,7 @@
  * @return An initialized unbound prefix exception
  */
 - initWithPrefix: (OFString*)prefix
 	  parser: (OFXMLParser*)parser;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFUndefinedKeyException.h
==================================================================
--- src/exceptions/OFUndefinedKeyException.h
+++ src/exceptions/OFUndefinedKeyException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFUndefinedKeyException \
  *	  OFUndefinedKeyException.h ObjFW/OFUndefinedKeyException.h
  *
  * @brief An exception indicating that a key for Key Value Coding is undefined.
@@ -90,5 +92,7 @@
  */
 - initWithObject: (id)object
 	     key: (OFString*)key
 	   value: (id)value;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFUnknownXMLEntityException.h
==================================================================
--- src/exceptions/OFUnknownXMLEntityException.h
+++ src/exceptions/OFUnknownXMLEntityException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFUnknownXMLEntityException \
  *	  OFUnknownXMLEntityException.h ObjFW/OFUnknownXMLEntityException.h
  *
  * @brief An exception indicating that a parser encountered an unknown XML
@@ -47,5 +49,7 @@
  * @param entityName The name of the unknown XML entity
  * @return An initialized unknown XML entity exception
  */
 - initWithEntityName: (OFString*)entityName;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFUnlockFailedException.h
==================================================================
--- src/exceptions/OFUnlockFailedException.h
+++ src/exceptions/OFUnlockFailedException.h
@@ -15,10 +15,12 @@
  */
 
 #import "OFException.h"
 #import "OFLocking.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFUnlockFailedException \
  *	  OFUnlockFailedException.h ObjFW/OFUnlockFailedException.h
  *
  * @brief An exception indicating that unlocking a lock failed.
@@ -29,23 +31,25 @@
 }
 
 /*!
  * The lock which could not be unlocked.
  */
-@property (readonly, nonatomic) id <OFLocking> lock;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic) id <OFLocking> lock;
 
 /*!
  * @brief Creates a new, autoreleased unlock failed exception.
  *
  * @param lock The lock which could not be unlocked
  * @return A new, autoreleased unlock failed exception
  */
-+ (instancetype)exceptionWithLock: (id <OFLocking>)lock;
++ (instancetype)exceptionWithLock: (nullable id <OFLocking>)lock;
 
 /*!
  * @brief Initializes an already allocated unlock failed exception.
  *
  * @param lock The lock which could not be unlocked
  * @return An initialized unlock failed exception
  */
-- initWithLock: (id <OFLocking>)lock;
+- initWithLock: (nullable id <OFLocking>)lock;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFUnsupportedProtocolException.h
==================================================================
--- src/exceptions/OFUnsupportedProtocolException.h
+++ src/exceptions/OFUnsupportedProtocolException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 @class OFURL;
 
 /*!
  * @class OFUnsupportedProtocolException \
  *	  OFUnsupportedProtocolException.h \
@@ -50,5 +52,7 @@
  * @param URL The URL whose protocol is unsupported
  * @return An initialized unsupported protocol exception
  */
 - initWithURL: (OFURL*)URL;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFUnsupportedVersionException.h
==================================================================
--- src/exceptions/OFUnsupportedVersionException.h
+++ src/exceptions/OFUnsupportedVersionException.h
@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFUnsupportedVersionException \
  *	  OFUnsupportedVersionException.h ObjFW/OFUnsupportedVersionException.h
  *
  * @brief An exception indicating that the specified version of the format or
@@ -47,5 +49,7 @@
  * @param version The version which is unsupported
  * @return An initialized unsupported version exception
  */
 - initWithVersion: (OFString*)version;
 @end
+
+OF_ASSUME_NONNULL_END

Index: src/exceptions/OFWriteFailedException.h
==================================================================
--- src/exceptions/OFWriteFailedException.h
+++ src/exceptions/OFWriteFailedException.h
@@ -14,13 +14,17 @@
  * file.
  */
 
 #import "OFReadOrWriteFailedException.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFWriteFailedException \
  *	  OFWriteFailedException.h ObjFW/OFWriteFailedException.h
  *
  * @brief An exception indicating that writing to an object failed.
  */
 @interface OFWriteFailedException: OFReadOrWriteFailedException
 @end
+
+OF_ASSUME_NONNULL_END