diff --git a/Framework/MIKMIDI.xcodeproj/project.pbxproj b/Framework/MIKMIDI.xcodeproj/project.pbxproj
index 134c39bc..b78977c8 100644
--- a/Framework/MIKMIDI.xcodeproj/project.pbxproj
+++ b/Framework/MIKMIDI.xcodeproj/project.pbxproj
@@ -255,6 +255,8 @@
 		9DB366F71A964D4A001D1CF3 /* MIKMIDISynthesizerInstrument.h in Headers */ = {isa = PBXBuildFile; fileRef = 9DB366F41A964D4A001D1CF3 /* MIKMIDISynthesizerInstrument.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		9DB366F81A964D4A001D1CF3 /* MIKMIDISynthesizerInstrument.m in Sources */ = {isa = PBXBuildFile; fileRef = 9DB366F51A964D4A001D1CF3 /* MIKMIDISynthesizerInstrument.m */; };
 		9DB366F91A964D4A001D1CF3 /* MIKMIDISynthesizerInstrument.m in Sources */ = {isa = PBXBuildFile; fileRef = 9DB366F51A964D4A001D1CF3 /* MIKMIDISynthesizerInstrument.m */; };
+		9DB8CD421BF266FE00F6388D /* MIKMIDIMetaEvent_SubclassMethods.h in Headers */ = {isa = PBXBuildFile; fileRef = 9DB8CD401BF266FE00F6388D /* MIKMIDIMetaEvent_SubclassMethods.h */; };
+		9DB8CD431BF266FE00F6388D /* MIKMIDIMetaEvent_SubclassMethods.h in Headers */ = {isa = PBXBuildFile; fileRef = 9DB8CD401BF266FE00F6388D /* MIKMIDIMetaEvent_SubclassMethods.h */; };
 		9DBEBD581AAA21BE00E59734 /* MIKMIDICommand_SubclassMethods.h in Headers */ = {isa = PBXBuildFile; fileRef = 9D74EF3517A713A100BEE89F /* MIKMIDICommand_SubclassMethods.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		9DBEBD591AAA21BE00E59734 /* MIKMIDICommand_SubclassMethods.h in Headers */ = {isa = PBXBuildFile; fileRef = 9D74EF3517A713A100BEE89F /* MIKMIDICommand_SubclassMethods.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		9DBEBD5A1AAA21C400E59734 /* MIKMIDIEvent_SubclassMethods.h in Headers */ = {isa = PBXBuildFile; fileRef = 839D932D19C3A2C9007589C3 /* MIKMIDIEvent_SubclassMethods.h */; settings = {ATTRIBUTES = (Public, ); }; };
@@ -446,6 +448,7 @@
 		9DB366EF1A964C55001D1CF3 /* MIKMIDISynthesizer.m */ = {isa = PBXFileReference; fileEncoding = 4; indentWidth = 4; lastKnownFileType = sourcecode.c.objc; path = MIKMIDISynthesizer.m; sourceTree = "<group>"; tabWidth = 4; usesTabs = 1; wrapsLines = 1; };
 		9DB366F41A964D4A001D1CF3 /* MIKMIDISynthesizerInstrument.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MIKMIDISynthesizerInstrument.h; sourceTree = "<group>"; };
 		9DB366F51A964D4A001D1CF3 /* MIKMIDISynthesizerInstrument.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MIKMIDISynthesizerInstrument.m; sourceTree = "<group>"; };
+		9DB8CD401BF266FE00F6388D /* MIKMIDIMetaEvent_SubclassMethods.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MIKMIDIMetaEvent_SubclassMethods.h; sourceTree = "<group>"; };
 		9DBEBD5C1AAA27D100E59734 /* module.modulemap */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = "sourcecode.module-map"; path = module.modulemap; sourceTree = SOURCE_ROOT; };
 		9DBEBD651AAA303700E59734 /* MIKMIDIChannelPressureEvent.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MIKMIDIChannelPressureEvent.h; sourceTree = "<group>"; };
 		9DBEBD661AAA303700E59734 /* MIKMIDIChannelPressureEvent.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MIKMIDIChannelPressureEvent.m; sourceTree = "<group>"; };
@@ -700,6 +703,7 @@
 			isa = PBXGroup;
 			children = (
 				839D933B19C3A2F5007589C3 /* MIKMIDIMetaEvent.h */,
+				9DB8CD401BF266FE00F6388D /* MIKMIDIMetaEvent_SubclassMethods.h */,
 				839D933C19C3A2F5007589C3 /* MIKMIDIMetaEvent.m */,
 				839D933719C3A2F5007589C3 /* MIKMIDIMetaCopyrightEvent.h */,
 				839D933819C3A2F5007589C3 /* MIKMIDIMetaCopyrightEvent.m */,
@@ -861,6 +865,7 @@
 				9D74EF7117A713A100BEE89F /* MIKMIDIEndpoint.h in Headers */,
 				83FB360E1B42D58000F91DCD /* MIKMIDISequence+MIKMIDIPrivate.h in Headers */,
 				9D74EF7317A713A100BEE89F /* MIKMIDIEntity.h in Headers */,
+				9DB8CD421BF266FE00F6388D /* MIKMIDIMetaEvent_SubclassMethods.h in Headers */,
 				9D74EF7517A713A100BEE89F /* MIKMIDIErrors.h in Headers */,
 				9D74EF7717A713A100BEE89F /* MIKMIDIInputPort.h in Headers */,
 				9D74EF7917A713A100BEE89F /* MIKMIDIMapping.h in Headers */,
@@ -948,6 +953,7 @@
 				9DAF8B631A7B008A00F46528 /* MIKMIDINoteOnCommand.h in Headers */,
 				9D84951D1AA7678700C52475 /* MIKMIDIProgramChangeEvent.h in Headers */,
 				9DAF8B5E1A7B007300F46528 /* MIKMIDIDestinationEndpoint.h in Headers */,
+				9DB8CD431BF266FE00F6388D /* MIKMIDIMetaEvent_SubclassMethods.h in Headers */,
 				9D3781561AA407A7007A61BE /* MIKMIDIResponder.h in Headers */,
 				9DAF8B7B1A7B00A700F46528 /* MIKMIDIPlayer.h in Headers */,
 				9DAF8B781A7B00A700F46528 /* MIKMIDIMetaTimeSignatureEvent.h in Headers */,
diff --git a/Source/MIKMIDIChannelEvent.h b/Source/MIKMIDIChannelEvent.h
index 11ed8858..78f313d9 100644
--- a/Source/MIKMIDIChannelEvent.h
+++ b/Source/MIKMIDIChannelEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import <MIKMIDI/MIKMIDIEvent.h>
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 @interface MIKMIDIChannelEvent : MIKMIDIEvent
 
@@ -18,7 +21,7 @@
  *
  *  @return A new instance of a subclass of MIKMIDIChannelEvent, or nil if there is an error.
  */
-+ (instancetype)channelEventWithTimeStamp:(MusicTimeStamp)timeStamp message:(MIDIChannelMessage)message;
++ (nullable instancetype)channelEventWithTimeStamp:(MusicTimeStamp)timeStamp message:(MIDIChannelMessage)message;
 
 // Properties
 
@@ -45,21 +48,27 @@
 @interface MIKMutableMIDIChannelEvent : MIKMIDIChannelEvent
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
-@property (nonatomic, strong, readwrite) NSMutableData *data;
+@property (nonatomic, strong, readwrite, null_resettable) NSMutableData *data;
 @property (nonatomic, readwrite) UInt8 channel;
 @property (nonatomic, readwrite) UInt8 dataByte1;
 @property (nonatomic, readwrite) UInt8 dataByte2;
 
 @end
 
+NS_ASSUME_NONNULL_END
+
 #pragma mark -
 
 #import <MIKMIDI/MIKMIDICommand.h>
 
 @class MIKMIDIClock;
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface MIKMIDICommand (MIKMIDIChannelEventToCommands)
 
-+ (instancetype)commandFromChannelEvent:(MIKMIDIChannelEvent *)event clock:(MIKMIDIClock *)clock;
++ (nullable instancetype)commandFromChannelEvent:(MIKMIDIChannelEvent *)event clock:(MIKMIDIClock *)clock;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIChannelPressureEvent.h b/Source/MIKMIDIChannelPressureEvent.h
index be1dc309..27ba7afd 100644
--- a/Source/MIKMIDIChannelPressureEvent.h
+++ b/Source/MIKMIDIChannelPressureEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIChannelEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A channel pressure (aftertouch) event.
@@ -32,9 +35,11 @@
 @property (nonatomic, readwrite) UInt8 pressure;
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
-@property (nonatomic, strong, readwrite) NSMutableData *data;
+@property (nonatomic, strong, readwrite, null_resettable) NSMutableData *data;
 @property (nonatomic, readwrite) UInt8 channel;
 @property (nonatomic, readwrite) UInt8 dataByte1;
 @property (nonatomic, readwrite) UInt8 dataByte2;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIChannelVoiceCommand.h b/Source/MIKMIDIChannelVoiceCommand.h
index 72030f16..93e606d6 100644
--- a/Source/MIKMIDIChannelVoiceCommand.h
+++ b/Source/MIKMIDIChannelVoiceCommand.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDICommand.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  MIKMIDIChannelVoiceCommand is used to represent MIDI messages whose type is
@@ -46,6 +49,8 @@
 @property (nonatomic, readwrite) UInt8 dataByte2;
 
 @property (nonatomic, readwrite) MIDITimeStamp midiTimestamp;
-@property (nonatomic, copy, readwrite) NSData *data;
+@property (nonatomic, copy, readwrite, null_resettable) NSData *data;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIChannelVoiceCommand_SubclassMethods.h b/Source/MIKMIDIChannelVoiceCommand_SubclassMethods.h
index 1c680abc..7806d69f 100644
--- a/Source/MIKMIDIChannelVoiceCommand_SubclassMethods.h
+++ b/Source/MIKMIDIChannelVoiceCommand_SubclassMethods.h
@@ -8,9 +8,14 @@
 
 #import "MIKMIDIChannelVoiceCommand.h"
 #import "MIKMIDICommand_SubclassMethods.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 @interface MIKMIDIChannelVoiceCommand ()
 
 @property (nonatomic, readwrite) NSUInteger value;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIClientDestinationEndpoint.h b/Source/MIKMIDIClientDestinationEndpoint.h
index 7559b9a8..66f70397 100644
--- a/Source/MIKMIDIClientDestinationEndpoint.h
+++ b/Source/MIKMIDIClientDestinationEndpoint.h
@@ -7,9 +7,12 @@
 //
 
 #import "MIKMIDIDestinationEndpoint.h"
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDIClientDestinationEndpoint;
 
+NS_ASSUME_NONNULL_BEGIN
+
 typedef void(^MIKMIDIClientDestinationEndpointEventHandler)(MIKMIDIClientDestinationEndpoint *destination, NSArray *commands);
 
 /**
@@ -37,11 +40,13 @@ typedef void(^MIKMIDIClientDestinationEndpointEventHandler)(MIKMIDIClientDestina
  *
  *  @return An instance of MIKMIDIClientDestinationEndpoint, or nil if an error occurs.
  */
-- (instancetype)initWithName:(NSString *)name receivedMessagesHandler:(MIKMIDIClientDestinationEndpointEventHandler)handler;
+- (nullable instancetype)initWithName:(NSString *)name receivedMessagesHandler:(nullable MIKMIDIClientDestinationEndpointEventHandler)handler;
 
 /**
  *  A block to be called when the receiver receives new incoming MIDI messages.
  */
-@property (nonatomic, strong) MIKMIDIClientDestinationEndpointEventHandler receivedMessagesHandler;
+@property (nonatomic, strong, nullable) MIKMIDIClientDestinationEndpointEventHandler receivedMessagesHandler;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIClientSourceEndpoint.h b/Source/MIKMIDIClientSourceEndpoint.h
index 887be9a3..c4411947 100644
--- a/Source/MIKMIDIClientSourceEndpoint.h
+++ b/Source/MIKMIDIClientSourceEndpoint.h
@@ -6,6 +6,9 @@
 //
 
 #import "MIKMIDISourceEndpoint.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *	MIKMIDIClientSourceEndpoint represents a virtual endpoint created by your application to send MIDI
@@ -27,7 +30,7 @@
  *
  *  @return An instance of MIKMIDIClientSourceEndpoint, or nil if an error occurs.
  */
-- (instancetype)initWithName:(NSString*)name;
+- (nullable instancetype)initWithName:(NSString *)name;
 
 /**
  *  Used to send MIDI messages/commands from your application to a MIDI output endpoint.
@@ -41,3 +44,5 @@
 - (BOOL)sendCommands:(NSArray *)commands error:(NSError **)error;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIClock.h b/Source/MIKMIDIClock.h
index 68966534..13a0e0fa 100644
--- a/Source/MIKMIDIClock.h
+++ b/Source/MIKMIDIClock.h
@@ -8,6 +8,7 @@
 
 #import <Foundation/Foundation.h>
 #import <AudioToolbox/AudioToolbox.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 /**
  *  Returns the number of MIDITimeStamps that would occur during a specified time interval.
@@ -25,6 +26,7 @@ Float64 MIKMIDIClockMIDITimeStampsPerTimeInterval(NSTimeInterval timeInterval);
  */
 Float64 MIKMIDIClockSecondsPerMIDITimeStamp();
 
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  MIKMIDIClock provides the number of seconds per MIDITimeStamp, as well as the
@@ -213,6 +215,6 @@ Float64 MIKMIDIClockSecondsPerMIDITimeStamp();
  */
 + (Float64)midiTimeStampsPerTimeInterval:(NSTimeInterval)timeInterval DEPRECATED_ATTRIBUTE;
 
-
 @end
 
+NS_ASSUME_NONNULL_END
diff --git a/Source/MIKMIDICommand.h b/Source/MIKMIDICommand.h
index 3bea78d9..9799b179 100644
--- a/Source/MIKMIDICommand.h
+++ b/Source/MIKMIDICommand.h
@@ -8,6 +8,7 @@
 
 #import <Foundation/Foundation.h>
 #import <CoreMIDI/CoreMIDI.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 /**
  *  Types of MIDI messages. These values correspond directly to the MIDI command type values
@@ -56,6 +57,8 @@ typedef NS_ENUM(NSUInteger, MIKMIDICommandType) {
 
 @class MIKMIDIMappingItem;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  In MIKMIDI, MIDI messages are objects. Specifically, they are instances of MIKMIDICommand or one of its
  *  subclasses. MIKMIDICommand's subclasses each represent a specific type of MIDI message, for example,
@@ -193,14 +196,14 @@ typedef NS_ENUM(NSUInteger, MIKMIDICommandType) {
 /**
  *  The raw data that makes up the receiver.
  */
-@property (nonatomic, copy, readonly) NSData *data;
+@property (nonatomic, copy, readonly, null_resettable) NSData *data;
 
 /**
  *  Optional mapping item used to route the command. This must be set by client code that handles
  *  receiving MIDI commands. Allows responders to understand how a command was mapped, especially
  *  useful to determine interaction type so that responders can interpret the command correctly.
  */
-@property (nonatomic, strong) MIKMIDIMappingItem *mappingItem;
+@property (nonatomic, strong, nullable) MIKMIDIMappingItem *mappingItem;
 
 @end
 
@@ -225,11 +228,12 @@ typedef NS_ENUM(NSUInteger, MIKMIDICommandType) {
  *  transfered to the caller which becomes responsible for freeing the allocated memory.
  *  Used by MIKMIDI when sending commands. Typically, this is not needed by clients of MIKMIDI.
  *
- *  @param outPacketList   A pointer pointer to a MIDIPacketList structure which will point to the created MIDIPacketList
+ *  @param outPacketList   A pointer to a pointer to a MIDIPacketList structure which will point to the created MIDIPacketList
  *                         upon success.
  *  @param commands        An array of MIKMIDICommand instances.
  *
  *  @return YES if creating the packet list was successful, NO if an error occurred.
  */
-BOOL MIKCreateMIDIPacketListFromCommands(MIDIPacketList **outPacketList, NSArray *commands);
+BOOL MIKCreateMIDIPacketListFromCommands(MIDIPacketList * _Nonnull * _Nonnull outPacketList, NSArray *commands);
 
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDICommand.m b/Source/MIKMIDICommand.m
index 6aed4ada..0969b510 100644
--- a/Source/MIKMIDICommand.m
+++ b/Source/MIKMIDICommand.m
@@ -298,7 +298,7 @@ - (void)setData:(NSData *)data
 {
 	if (![[self class] isMutable]) return MIKMIDI_RAISE_MUTATION_ATTEMPT_EXCEPTION;
 	
-	self.internalData = [data mutableCopy];
+	self.internalData = data ? [data mutableCopy] : [NSMutableData data];
 }
 
 @end
diff --git a/Source/MIKMIDICommandScheduler.h b/Source/MIKMIDICommandScheduler.h
index abfd4e56..496ac728 100644
--- a/Source/MIKMIDICommandScheduler.h
+++ b/Source/MIKMIDICommandScheduler.h
@@ -7,7 +7,9 @@
 //
 
 #import <Foundation/Foundation.h>
+#import "MIKMIDICompilerCompatibility.h"
 
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *	Objects that conform to this protocol can be used as a destination for MIDI commands to
@@ -20,3 +22,5 @@
 - (void)scheduleMIDICommands:(NSArray *)commands;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/Source/MIKMIDICommandThrottler.h b/Source/MIKMIDICommandThrottler.h
index 380976c1..bcf45673 100644
--- a/Source/MIKMIDICommandThrottler.h
+++ b/Source/MIKMIDICommandThrottler.h
@@ -7,14 +7,16 @@
 //
 
 #import <Foundation/Foundation.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDIChannelVoiceCommand;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  MIKMIDICommandThrottler is a simple utility class useful for throttling e.g. jog wheel/turntable controls, 
  *  which otherwise send many messages per revolution.
  */
-
 @interface MIKMIDICommandThrottler : NSObject
 
 /**
@@ -35,3 +37,5 @@
 - (void)resetThrottlingCountForCommand:(MIKMIDIChannelVoiceCommand *)command;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/Source/MIKMIDIControlChangeCommand.h b/Source/MIKMIDIControlChangeCommand.h
index 5f094e9f..d1b0f6b9 100644
--- a/Source/MIKMIDIControlChangeCommand.h
+++ b/Source/MIKMIDIControlChangeCommand.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIChannelVoiceCommand.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A MIDI control change message.
@@ -33,7 +36,7 @@
  *  @return A new, single MIKMIDIControlChangeCommand instance containing 14-bit value data, and whose 
  *  fourteenBitCommand property is set to YES.
  */
-+ (instancetype)commandByCoalescingMSBCommand:(MIKMIDIControlChangeCommand *)msbCommand andLSBCommand:(MIKMIDIControlChangeCommand *)lsbCommand;
++ (nullable instancetype)commandByCoalescingMSBCommand:(MIKMIDIControlChangeCommand *)msbCommand andLSBCommand:(MIKMIDIControlChangeCommand *)lsbCommand;
 
 /**
  *  The MIDI control number for the command.
@@ -101,6 +104,8 @@
 @property (nonatomic, readwrite) UInt8 dataByte2;
 
 @property (nonatomic, readwrite) MIDITimeStamp midiTimestamp;
-@property (nonatomic, copy, readwrite) NSData *data;
+@property (nonatomic, copy, readwrite, null_resettable) NSData *data;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIControlChangeEvent.h b/Source/MIKMIDIControlChangeEvent.h
index 0f5b1cbe..30bd79f1 100644
--- a/Source/MIKMIDIControlChangeEvent.h
+++ b/Source/MIKMIDIControlChangeEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIChannelEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  Control change events are typically sent when a controller value changes. 
@@ -40,9 +43,11 @@
 @property (nonatomic, readwrite) NSUInteger controllerValue;
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
-@property (nonatomic, strong, readwrite) NSMutableData *data;
+@property (nonatomic, strong, readwrite, null_resettable) NSMutableData *data;
 @property (nonatomic, readwrite) UInt8 channel;
 @property (nonatomic, readwrite) UInt8 dataByte1;
 @property (nonatomic, readwrite) UInt8 dataByte2;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIDestinationEndpoint.h b/Source/MIKMIDIDestinationEndpoint.h
index 31ed3de3..77993f56 100644
--- a/Source/MIKMIDIDestinationEndpoint.h
+++ b/Source/MIKMIDIDestinationEndpoint.h
@@ -8,6 +8,9 @@
 
 #import "MIKMIDIEndpoint.h"
 #import "MIKMIDICommandScheduler.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  MIKMIDIDestinationEndpoint represents a source (input) MIDI endpoint.
@@ -36,3 +39,5 @@
 - (void)unscheduleAllPendingEvents;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIEndpoint.h b/Source/MIKMIDIEndpoint.h
index b32d98a9..4faccd49 100644
--- a/Source/MIKMIDIEndpoint.h
+++ b/Source/MIKMIDIEndpoint.h
@@ -7,9 +7,12 @@
 //
 
 #import "MIKMIDIObject.h"
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDIEntity;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  Base class for MIDI endpoint objects. Not used directly, rather, in use, instances will always be
  *  instances of MIKMIDISourceEndpoint or MIKMIDIDestinationEndpoint.
@@ -19,7 +22,7 @@
 /**
  *  The entity that contains the receiver. Will be nil for non-wrapped virtual endpoints.
  */
-@property (nonatomic, weak, readonly) MIKMIDIEntity *entity;
+@property (nonatomic, weak, readonly, nullable) MIKMIDIEntity *entity;
 
 /**
  *  Whether or not the endpoint is private or hidden. See kMIDIPropertyPrivate in MIDIServices.h.
@@ -27,3 +30,5 @@
 @property (nonatomic, readonly) BOOL isPrivate;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIEndpointSynthesizer.h b/Source/MIKMIDIEndpointSynthesizer.h
index 9f84ffca..d59dd097 100644
--- a/Source/MIKMIDIEndpointSynthesizer.h
+++ b/Source/MIKMIDIEndpointSynthesizer.h
@@ -7,12 +7,15 @@
 //
 
 #import "MIKMIDISynthesizer.h"
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDIEndpoint;
 @class MIKMIDISourceEndpoint;
 @class MIKMIDIClientDestinationEndpoint;
 @class MIKMIDISynthesizerInstrument;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  MIKMIDIEndpointSynthesizer is a subclass of MIKMIDISynthesizer that
  *  provides a very simple way to synthesize MIDI commands coming from a
@@ -33,7 +36,7 @@
  *
  *  @return An initialized MIKMIDIEndpointSynthesizer or nil if an error occurs.
  */
-+ (instancetype)playerWithMIDISource:(MIKMIDISourceEndpoint *)source;
++ (nullable instancetype)playerWithMIDISource:(MIKMIDISourceEndpoint *)source;
 
 /**
  *  Creates and initializes an MIKMIDIEndpointSynthesizer instance.
@@ -44,7 +47,7 @@
  *
  *  @return An initialized MIKMIDIEndpointSynthesizer or nil if an error occurs.
  */
-+ (instancetype)playerWithMIDISource:(MIKMIDISourceEndpoint *)source componentDescription:(AudioComponentDescription)componentDescription;
++ (nullable instancetype)playerWithMIDISource:(MIKMIDISourceEndpoint *)source componentDescription:(AudioComponentDescription)componentDescription;
 
 /**
  *  Initializes an MIKMIDIEndpointSynthesizer instance using Apple's DLS synth as the
@@ -54,7 +57,7 @@
  *
  *  @return An initialized MIKMIDIEndpointSynthesizer or nil if an error occurs.
  */
-- (instancetype)initWithMIDISource:(MIKMIDISourceEndpoint *)source;
+- (nullable instancetype)initWithMIDISource:(MIKMIDISourceEndpoint *)source;
 
 /**
  *  Initializes an MIKMIDIEndpointSynthesizer instance.
@@ -65,7 +68,7 @@
  *
  *  @return An initialized MIKMIDIEndpointSynthesizer or nil if an error occurs.
  */
-- (instancetype)initWithMIDISource:(MIKMIDISourceEndpoint *)source componentDescription:(AudioComponentDescription)componentDescription;
+- (nullable instancetype)initWithMIDISource:(MIKMIDISourceEndpoint *)source componentDescription:(AudioComponentDescription)componentDescription;
 
 /**
  *  Creates and initializes an MIKMIDIEndpointSynthesizer instance using Apple's DLS synth as the
@@ -75,7 +78,7 @@
  *
  *  @return An initialized MIKMIDIEndpointSynthesizer or nil if an error occurs.
  */
-+ (instancetype)synthesizerWithClientDestinationEndpoint:(MIKMIDIClientDestinationEndpoint *)destination;
++ (nullable instancetype)synthesizerWithClientDestinationEndpoint:(MIKMIDIClientDestinationEndpoint *)destination;
 
 /**
  *  Creates and initializes an MIKMIDIEndpointSynthesizer instance.
@@ -86,7 +89,7 @@
  *
  *  @return An initialized MIKMIDIEndpointSynthesizer or nil if an error occurs.
  */
-+ (instancetype)synthesizerWithClientDestinationEndpoint:(MIKMIDIClientDestinationEndpoint *)destination componentDescription:(AudioComponentDescription)componentDescription;
++ (nullable instancetype)synthesizerWithClientDestinationEndpoint:(MIKMIDIClientDestinationEndpoint *)destination componentDescription:(AudioComponentDescription)componentDescription;
 
 /**
  *  Initializes an MIKMIDIEndpointSynthesizer instance using Apple's DLS synth as the
@@ -96,7 +99,7 @@
  *
  *  @return An initialized MIKMIDIEndpointSynthesizer or nil if an error occurs.
  */
-- (instancetype)initWithClientDestinationEndpoint:(MIKMIDIClientDestinationEndpoint *)destination;
+- (nullable instancetype)initWithClientDestinationEndpoint:(MIKMIDIClientDestinationEndpoint *)destination;
 
 /**
  *  Initializes an MIKMIDIEndpointSynthesizer instance.
@@ -107,7 +110,7 @@
  *
  *  @return An initialized MIKMIDIEndpointSynthesizer or nil if an error occurs.
  */
-- (instancetype)initWithClientDestinationEndpoint:(MIKMIDIClientDestinationEndpoint *)destination componentDescription:(AudioComponentDescription)componentDescription;
+- (nullable instancetype)initWithClientDestinationEndpoint:(MIKMIDIClientDestinationEndpoint *)destination componentDescription:(AudioComponentDescription)componentDescription;
 
 // Properties
 
@@ -117,7 +120,8 @@
  *  events coming from an external MIDI keyboard, or it may be an MIKMIDIClientDestinationEndpoint,
  *  e.g. to synthesize MIDI events coming from an another application on the system.
  */
-@property (nonatomic, strong, readonly) MIKMIDIEndpoint *endpoint;
+@property (nonatomic, strong, readonly, nullable) MIKMIDIEndpoint *endpoint;
 
 @end
 
+NS_ASSUME_NONNULL_END
diff --git a/Source/MIKMIDIEndpointSynthesizer.m b/Source/MIKMIDIEndpointSynthesizer.m
index 098f6de1..4cbf91c7 100644
--- a/Source/MIKMIDIEndpointSynthesizer.m
+++ b/Source/MIKMIDIEndpointSynthesizer.m
@@ -93,12 +93,10 @@ - (instancetype)initWithClientDestinationEndpoint:(MIKMIDIClientDestinationEndpo
 
 - (void)dealloc
 {
-	if (_endpoint) {
-		if ([_endpoint isKindOfClass:[MIKMIDISourceEndpoint class]]) {
-			[[MIKMIDIDeviceManager sharedDeviceManager] disconnectConnectionforToken:self.connectionToken];
-		}
-		// Don't need to do anything for a destination endpoint. __weak reference in the messages handler will automatically nil out.
+	if ([_endpoint isKindOfClass:[MIKMIDISourceEndpoint class]]) {
+		[[MIKMIDIDeviceManager sharedDeviceManager] disconnectConnectionforToken:self.connectionToken];
 	}
+	// Don't need to do anything for a destination endpoint. __weak reference in the messages handler will automatically nil out.
 }
 
 #pragma mark - Private
diff --git a/Source/MIKMIDIEvent.h b/Source/MIKMIDIEvent.h
index c60ddd73..fcea9c6c 100644
--- a/Source/MIKMIDIEvent.h
+++ b/Source/MIKMIDIEvent.h
@@ -8,6 +8,7 @@
 
 #import <Foundation/Foundation.h>
 #import <AudioToolbox/AudioToolbox.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 /**
  *  Types of MIDI events. These values are used to determine which subclass to
@@ -89,6 +90,8 @@ typedef NS_ENUM(NSUInteger, MIKMIDIMetaEventTypeType)
     MIKMIDIMetaEventTypeSequencerSpecificEvent  = 0x7F
 };
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  In MIKMIDI, MIDI events are objects. Specifically, they are instances of MIKMIDIEvent or one of its
  *  subclasses. MIKMIDIEvent's subclasses each represent a specific type of MIDI event, for example,
@@ -155,7 +158,7 @@ typedef NS_ENUM(NSUInteger, MIKMIDIMetaEventTypeType)
  *
  *  @see +mikEventTypeForMusicEventType:
  */
-+ (instancetype)midiEventWithTimeStamp:(MusicTimeStamp)timeStamp eventType:(MusicEventType)eventType data:(NSData *)data;
++ (nullable instancetype)midiEventWithTimeStamp:(MusicTimeStamp)timeStamp eventType:(MusicEventType)eventType data:(nullable NSData *)data;
 
 /**
  *  Initializes a new MIKMIDIEvent subclass instance. This method may return an instance of a different class than the
@@ -168,7 +171,7 @@ typedef NS_ENUM(NSUInteger, MIKMIDIMetaEventTypeType)
  *  @return For supported command types, an initialized MIKMIDIEvent subclass. Otherwise, an instance of
  *	MIKMIDICommand itself. nil if there is an error.
  */
-- (instancetype)initWithTimeStamp:(MusicTimeStamp)timeStamp midiEventType:(MIKMIDIEventType)eventType data:(NSData *)data NS_DESIGNATED_INITIALIZER;
+- (nullable instancetype)initWithTimeStamp:(MusicTimeStamp)timeStamp midiEventType:(MIKMIDIEventType)eventType data:(nullable NSData *)data NS_DESIGNATED_INITIALIZER;
 
 /**
  *  The MIDI event type.
@@ -196,18 +199,24 @@ typedef NS_ENUM(NSUInteger, MIKMIDIMetaEventTypeType)
 
 @property (nonatomic, readonly) MIKMIDIEventType eventType;
 @property (nonatomic) MusicTimeStamp timeStamp;
-@property (nonatomic, strong, readwrite) NSMutableData *data;
+@property (nonatomic, strong, readwrite, null_resettable) NSMutableData *data;
 
 @end
 
+NS_ASSUME_NONNULL_END
+
 #pragma mark - MIKMIDICommand+MIKMIDIEventToCommands
 
 #import <MIKMIDI/MIKMIDICommand.h>
 
 @class MIKMIDIClock;
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface MIKMIDICommand (MIKMIDIEventToCommands)
 
 + (NSArray *)commandsFromMIDIEvent:(MIKMIDIEvent *)event clock:(MIKMIDIClock *)clock;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIEvent.m b/Source/MIKMIDIEvent.m
index 37767edf..0b125734 100644
--- a/Source/MIKMIDIEvent.m
+++ b/Source/MIKMIDIEvent.m
@@ -253,7 +253,7 @@ - (NSData *)data { return [self.internalData copy]; }
 - (void)setData:(NSData *)data
 {
 	if (![[self class] isMutable]) return MIKMIDI_RAISE_MUTATION_ATTEMPT_EXCEPTION;
-	self.internalData = [data mutableCopy];
+	self.internalData = data ? [data mutableCopy] : [NSMutableData data];
 }
 
 - (void)setTimeStamp:(MusicTimeStamp)timeStamp
@@ -262,6 +262,13 @@ - (void)setTimeStamp:(MusicTimeStamp)timeStamp
 	_timeStamp = timeStamp;
 }
 
+- (void)setInternalData:(NSMutableData *)internalData
+{
+	if (internalData != _internalData) {
+		_internalData = internalData ? [internalData mutableCopy] : [NSMutableData data];
+	}
+}
+
 @end
 
 @implementation MIKMutableMIDIEvent
diff --git a/Source/MIKMIDIEventIterator.h b/Source/MIKMIDIEventIterator.h
index 61e2c958..21f09642 100644
--- a/Source/MIKMIDIEventIterator.h
+++ b/Source/MIKMIDIEventIterator.h
@@ -8,10 +8,13 @@
 
 #import <Foundation/Foundation.h>
 #import <AudioToolbox/AudioToolbox.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDITrack;
 @class MIKMIDIEvent;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  MIKMIDIEventIterator is an Objective-C wrapper for CoreMIDI's MusicEventIterator. It is not intended for use by clients/users of
  *  of MIKMIDI. Rather, it should be thought of as an MIKMIDI private class.
@@ -21,10 +24,10 @@
 @property (nonatomic, readonly) BOOL hasPreviousEvent;
 @property (nonatomic, readonly) BOOL hasCurrentEvent;
 @property (nonatomic, readonly) BOOL hasNextEvent;
-@property (nonatomic, readonly) MIKMIDIEvent *currentEvent;
+@property (nonatomic, readonly, nullable) MIKMIDIEvent *currentEvent;
 
-- (instancetype)initWithTrack:(MIKMIDITrack *)track;
-+ (instancetype)iteratorForTrack:(MIKMIDITrack *)track;
+- (nullable instancetype)initWithTrack:(MIKMIDITrack *)track;
++ (nullable instancetype)iteratorForTrack:(MIKMIDITrack *)track;
 
 - (BOOL)seek:(MusicTimeStamp)timeStamp;
 - (BOOL)moveToNextEvent;
@@ -33,3 +36,5 @@
 - (BOOL)moveCurrentEventTo:(MusicTimeStamp)timestamp error:(NSError **)error;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIEvent_SubclassMethods.h b/Source/MIKMIDIEvent_SubclassMethods.h
index e5a4ef47..49c45ea3 100644
--- a/Source/MIKMIDIEvent_SubclassMethods.h
+++ b/Source/MIKMIDIEvent_SubclassMethods.h
@@ -6,6 +6,10 @@
 //  Copyright (c) 2014 Mixed In Key. All rights reserved.
 //
 
+#import "MIKMIDIEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 @interface MIKMIDIEvent ()
 
@@ -77,15 +81,12 @@
  *  data property. Subclasses may set it. When mutating it, subclasses should manually
  *  call -will/didChangeValueForKey for the internalData key path.
  */
-@property (nonatomic, strong, readwrite) NSMutableData *internalData;
+@property (nonatomic, strong /* mutableCopy*/, readwrite) NSMutableData *internalData;
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 
 @property (nonatomic, readwrite) MIKMIDIEventType eventType;
 
-@property (nonatomic, strong, readwrite) NSData *metaData;
-
-
 /**
  *  Additional description string to be appended to basic description provided by
  *  -[MIKMIDIEvent description]. Subclasses of MIKMIDIEvent can override this
@@ -109,4 +110,6 @@
  */
 + (BOOL)supportsMIKMIDIEventType:(MIKMIDIEventType)type DEPRECATED_ATTRIBUTE;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIInputPort.m b/Source/MIKMIDIInputPort.m
index 7aab44ee..f0cfab66 100644
--- a/Source/MIKMIDIInputPort.m
+++ b/Source/MIKMIDIInputPort.m
@@ -40,7 +40,7 @@ @interface MIKMIDIInputPort ()
 
 @implementation MIKMIDIInputPort
 
-- (id)initWithClient:(MIDIClientRef)clientRef name:(NSString *)name
+- (instancetype)initWithClient:(MIDIClientRef)clientRef name:(NSString *)name
 {
 	self = [super initWithClient:clientRef name:name];
 	if (self) {
diff --git a/Source/MIKMIDIMappableResponder.h b/Source/MIKMIDIMappableResponder.h
index 478e4811..4966ba54 100644
--- a/Source/MIKMIDIMappableResponder.h
+++ b/Source/MIKMIDIMappableResponder.h
@@ -8,6 +8,7 @@
 
 #import <Foundation/Foundation.h>
 #import "MIKMIDIResponder.h"
+#import "MIKMIDICompilerCompatibility.h"
 
 /**
  *  Bit-mask constants used to specify MIDI responder types for mapping.
@@ -82,6 +83,8 @@ typedef NS_OPTIONS(NSUInteger, MIKMIDIResponderType){
 	MIKMIDIResponderTypeAll = NSUIntegerMax,
 };
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  This protocol defines methods that that must be implemented by MIDI responder objects to be mapped
  *  using MIKMIDIMappingGenerator, and to whom MIDI messages will selectively be routed using a MIDI mapping
@@ -142,3 +145,5 @@ typedef NS_OPTIONS(NSUInteger, MIKMIDIResponderType){
 - (BOOL)illuminationStateForCommandIdentifier:(NSString *)commandID;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMapping.h b/Source/MIKMIDIMapping.h
index 6afd4d8d..fb0613f9 100644
--- a/Source/MIKMIDIMapping.h
+++ b/Source/MIKMIDIMapping.h
@@ -7,6 +7,7 @@
 //
 
 #import <Foundation/Foundation.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 #import "MIKMIDICommand.h"
 #import "MIKMIDIResponder.h"
@@ -16,6 +17,8 @@
 @class MIKMIDIChannelVoiceCommand;
 @class MIKMIDIMappingItem;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  Overview
  *  --------
@@ -79,27 +82,12 @@
 /**
  *  Initializes and returns an MIKMIDIMapping object created from the XML file at url.
  *
- *  @note This method is currently only available on OS X. See https://github.com/mixedinkey-opensource/MIKMIDI/issues/2
- *
  *  @param url   An NSURL for the file to be read.
  *  @param error If an error occurs, upon returns contains an NSError object that describes the problem. If you are not interested in possible errors, you may pass in NULL.
  *
  *  @return An initialized MIKMIDIMapping instance, or nil if an error occurred.
  */
-- (instancetype)initWithFileAtURL:(NSURL *)url error:(NSError **)error;
-
-/**
- *  Initializes and returns an MIKMIDIMapping object created from the XML file at url.
- *
- *  @note This method is currently only available on OS X. See https://github.com/mixedinkey-opensource/MIKMIDI/issues/2
- *
- *  @param url   An NSURL for the file to be read.
- *
- *  @return An initialized MIKMIDIMapping instance, or nil if an error occurred.
- *
- *  @see -initWithFileAtURL:error:
- */
-- (instancetype)initWithFileAtURL:(NSURL *)url;
+- (nullable instancetype)initWithFileAtURL:(NSURL *)url error:(NSError **)error;
 
 /**
  *	Creates and initializes an MIKMIDIMapping object that is the same as the passed in bundled mapping
@@ -132,11 +120,11 @@
  *  Returns an NSString instance containing an XML representation of the receiver.
  *  The XML document returned by this method can be written to disk.
  *
- *  @return An NSString containing an XML representation of the receiver.
+ *  @return An NSString containing an XML representation of the receiver, or nil if an error occurred.
  *
  *  @see -writeToFileAtURL:error:
  */
-- (NSString *)XMLStringRepresentation;
+- (nullable NSString *)XMLStringRepresentation;
 
 /**
  *  Writes the receiver as an XML file to the specified URL.
@@ -220,7 +208,7 @@
 /**
  *  Optional additional key value pairs, which will be saved as attributes in this mapping's XML representation. Keys and values must be NSStrings.
  */
-@property (nonatomic, copy) NSDictionary *additionalAttributes;
+@property (nonatomic, copy, nullable) NSDictionary *additionalAttributes;
 
 /**
  *  All mapping items this mapping contains.
@@ -256,3 +244,23 @@
 - (void)removeMappingItems:(NSSet *)mappingItems;
 
 @end
+
+#pragma mark - 
+
+@interface MIKMIDIMapping (Deprecated)
+
+/**
+ *  @deprecated Use -initWithFileAtURL:error: instead.
+ *  Initializes and returns an MIKMIDIMapping object created from the XML file at url.
+ *
+ *  @param url   An NSURL for the file to be read.
+ *
+ *  @return An initialized MIKMIDIMapping instance, or nil if an error occurred.
+ *
+ *  @see -initWithFileAtURL:error:
+ */
+- (nullable instancetype)initWithFileAtURL:(NSURL *)url DEPRECATED_ATTRIBUTE;
+
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMapping.m b/Source/MIKMIDIMapping.m
index af70b29d..a42e10a8 100644
--- a/Source/MIKMIDIMapping.m
+++ b/Source/MIKMIDIMapping.m
@@ -45,11 +45,6 @@ @interface MIKMIDIMapping ()
 
 @implementation MIKMIDIMapping
 
-- (instancetype)initWithFileAtURL:(NSURL *)url
-{
-	return [self initWithFileAtURL:url error:NULL];
-}
-
 - (instancetype)initWithFileAtURL:(NSURL *)url error:(NSError **)error;
 {
 	error = error ? error : &(NSError *__autoreleasing){ nil };
@@ -94,7 +89,7 @@ - (id)init
 {
     self = [super init];
     if (self) {
-        self.internalMappingItems = [NSMutableSet set];
+        _internalMappingItems = [NSMutableSet set];
     }
     return self;
 }
@@ -466,3 +461,14 @@ - (NSString *)name
 }
 
 @end
+
+#pragma mark -
+
+@implementation MIKMIDIMapping (Deprecated)
+
+- (instancetype)initWithFileAtURL:(NSURL *)url
+{
+	return [self initWithFileAtURL:url error:NULL];
+}
+
+@end
\ No newline at end of file
diff --git a/Source/MIKMIDIMappingGenerator.h b/Source/MIKMIDIMappingGenerator.h
index b71226b9..e466781f 100644
--- a/Source/MIKMIDIMappingGenerator.h
+++ b/Source/MIKMIDIMappingGenerator.h
@@ -7,7 +7,7 @@
 //
 
 #import <Foundation/Foundation.h>
-//#import "MIKMIDIPrivate.h"
+#import "MIKMIDICompilerCompatibility.h"
 
 #import "MIKMIDIMapping.h"
 
@@ -17,6 +17,8 @@
 
 @protocol MIKMIDIMappingGeneratorDelegate;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  Completion block for mapping generation method.
  *
@@ -24,7 +26,7 @@
  *  @param messages    The messages used to generate the mapping. May not include all messages received during mapping.
  *  @param error       If mapping failed, an NSError explaing the failure, nil if mapping succeeded.
  */
-typedef void(^MIKMIDIMappingGeneratorMappingCompletionBlock)(MIKMIDIMappingItem *mappingItem, NSArray *messages, NSError *error);
+typedef void(^MIKMIDIMappingGeneratorMappingCompletionBlock)(MIKMIDIMappingItem *mappingItem, NSArray *messages, NSError *_Nullable error);
 
 /**
  *  MIKMIDIMappingGenerator is used to map incoming commands from a MIDI device to MIDI responders in an application.
@@ -124,9 +126,9 @@ typedef void(^MIKMIDIMappingGeneratorMappingCompletionBlock)(MIKMIDIMappingItem
 @property (nonatomic, MIKMIDIMappingGeneratorWeakProperty) id<MIKMIDIMappingGeneratorDelegate> delegate;
 
 /**
- *  The device for which a mapping is being generated. Must not be nil.
+ *  The device for which a mapping is being generated. Must not be nil for mapping to work.
  */
-@property (nonatomic, strong) MIKMIDIDevice *device;
+@property (nonatomic, strong, nullable) MIKMIDIDevice *device;
 
 /**
  *  The mapping being generated. Assign before mapping starts to modify existing mapping.
@@ -233,4 +235,6 @@ shouldRemoveExistingMappingItems:(NSSet *)mappingItems
 - (MIKMIDIChannelVoiceCommand *)mappingGenerator:(MIKMIDIMappingGenerator *)generator
 			  commandByProcessingIncomingCommand:(MIKMIDIChannelVoiceCommand *)command;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMappingGenerator.m b/Source/MIKMIDIMappingGenerator.m
index ab1c27c5..7763904f 100644
--- a/Source/MIKMIDIMappingGenerator.m
+++ b/Source/MIKMIDIMappingGenerator.m
@@ -80,11 +80,9 @@ - (instancetype)initWithDevice:(MIKMIDIDevice *)device error:(NSError **)error;
 	return self;
 }
 
-- (id)init
+- (id)init NS_UNAVAILABLE
 {
 	[NSException raise:NSInternalInconsistencyException format:@"-initWithDevice: is the designated initializer for %@", NSStringFromClass([self class])];
-	self = [self initWithDevice:nil error:NULL]; // Keep the compiler happy
-	[self self]; // Keep the compiler happy part 2
 	return nil;
 }
 
diff --git a/Source/MIKMIDIMappingItem.h b/Source/MIKMIDIMappingItem.h
index f9dfaaff..fcf8b21f 100644
--- a/Source/MIKMIDIMappingItem.h
+++ b/Source/MIKMIDIMappingItem.h
@@ -9,9 +9,12 @@
 #import <Foundation/Foundation.h>
 #import "MIKMIDIMappableResponder.h"
 #import "MIKMIDICommand.h"
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDIMapping;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  MIKMIDIMappingItem contains information about a mapping between a physical MIDI control,
  *  and a single command supported by a particular MIDI responder object.
@@ -38,11 +41,11 @@
  *  Returns an NSString instance containing an XML representation of the receiver.
  *  The XML document returned by this method can be written to disk.
  *
- *  @return An NSString containing an XML representation of the receiver.
+ *  @return An NSString containing an XML representation of the receiver, or nil if an error occurred.
  *
  *  @see -writeToFileAtURL:error:
  */
-- (NSString *)XMLStringRepresentation;
+- (nullable NSString *)XMLStringRepresentation;
 
 // Properties
 
@@ -92,12 +95,14 @@
 /**
  *  Optional additional key value pairs, which will be saved as attributes in this item's XML representation. Keys and values must be NSStrings.
  */
-@property (nonatomic, copy) NSDictionary *additionalAttributes;
+@property (nonatomic, copy, nullable) NSDictionary *additionalAttributes;
 
 /**
  *  The MIDI Mapping the receiver belongs to. May be nil if the mappping item hasn't been added to a mapping yet,
  *  or its mapping has been deallocated.
  */
-@property (nonatomic, weak, readonly) MIKMIDIMapping *mapping;
+@property (nonatomic, weak, readonly, nullable) MIKMIDIMapping *mapping;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMappingManager.h b/Source/MIKMIDIMappingManager.h
index 995feacb..293daa6a 100644
--- a/Source/MIKMIDIMappingManager.h
+++ b/Source/MIKMIDIMappingManager.h
@@ -7,11 +7,14 @@
 //
 
 #import <Foundation/Foundation.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 #define kMIKMIDIMappingFileExtension @"midimap"
 
 @class MIKMIDIMapping;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  MIKMIDIMappingManager provides a centralized way to manage an application's
  *  MIDI mappings. It handles both bundled (built in) mapping files, as well
@@ -91,7 +94,7 @@
  *
  *  @return An MIKMIDIMapping instance for the imported file, or nil if there was an error.
  */
-- (MIKMIDIMapping *)importMappingFromFileAtURL:(NSURL *)URL overwritingExistingMapping:(BOOL)shouldOverwrite error:(NSError **)error;
+- (nullable MIKMIDIMapping *)importMappingFromFileAtURL:(NSURL *)URL overwritingExistingMapping:(BOOL)shouldOverwrite error:(NSError **)error;
 
 /**
  *  Saves user mappings to disk. These mappings are currently saved to a folder at <AppSupport>/<ApplicationBundleID>/MIDI Mappings.
@@ -155,6 +158,8 @@
  *
  *  @deprecated Deprecated. Use -mappingsWithName: instead.
  */
-- (MIKMIDIMapping *)mappingWithName:(NSString *)mappingName DEPRECATED_ATTRIBUTE;
+- (nullable MIKMIDIMapping *)mappingWithName:(NSString *)mappingName DEPRECATED_ATTRIBUTE;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMappingManager.m b/Source/MIKMIDIMappingManager.m
index 062cab1f..60a4e52a 100644
--- a/Source/MIKMIDIMappingManager.m
+++ b/Source/MIKMIDIMappingManager.m
@@ -226,7 +226,12 @@ - (void)loadAvailableUserMappings
 			if (![[file pathExtension] isEqualToString:kMIKMIDIMappingFileExtension]) continue;
 			
 			// process the mapping file
-			MIKMIDIMapping *mapping = [[MIKMIDIMapping alloc] initWithFileAtURL:file];
+			NSError *error = nil;
+			MIKMIDIMapping *mapping = [[MIKMIDIMapping alloc] initWithFileAtURL:file error:&error];
+			if (!mapping) {
+				NSLog(@"Error loading MIDI mapping from %@: %@", file, error);
+				continue;
+			}
 			if (mapping) [mappings addObject:mapping];
 		}
 	} else {
@@ -243,7 +248,12 @@ - (void)loadBundledMappings
 	NSBundle *bundle = [NSBundle mainBundle];
 	NSArray *bundledMappingFileURLs = [bundle URLsForResourcesWithExtension:kMIKMIDIMappingFileExtension subdirectory:nil];
 	for (NSURL *file in bundledMappingFileURLs) {
-		MIKMIDIMapping *mapping = [[MIKMIDIMapping alloc] initWithFileAtURL:file];
+		NSError *error = nil;
+		MIKMIDIMapping *mapping = [[MIKMIDIMapping alloc] initWithFileAtURL:file error:&error];
+		if (!mapping) {
+			NSLog(@"Error loading MIDI mapping from %@: %@", file, error);
+			continue;
+		}
 		mapping.bundledMapping = YES;
 		if (mapping) [mappings addObject:mapping];
 	}
diff --git a/Source/MIKMIDIMappingManager_SubclassMethods.h b/Source/MIKMIDIMappingManager_SubclassMethods.h
index d6855266..0788118b 100644
--- a/Source/MIKMIDIMappingManager_SubclassMethods.h
+++ b/Source/MIKMIDIMappingManager_SubclassMethods.h
@@ -8,9 +8,11 @@
 
 
 #import "MIKMIDIMappingManager.h"
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDIMapping;
 
+NS_ASSUME_NONNULL_BEGIN
 
 @interface MIKMIDIMappingManager ()
 
@@ -38,6 +40,8 @@
  *
  *	@return An array of legacy file names, or nil.
  */
-- (NSArray *)legacyFileNamesForUserMappingsObject:(MIKMIDIMapping *)mapping;
+- (nullable NSArray *)legacyFileNamesForUserMappingsObject:(MIKMIDIMapping *)mapping;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMappingXMLParser.h b/Source/MIKMIDIMappingXMLParser.h
index 5bdf5a8e..f699cdc6 100644
--- a/Source/MIKMIDIMappingXMLParser.h
+++ b/Source/MIKMIDIMappingXMLParser.h
@@ -7,9 +7,12 @@
 //
 
 #import <Foundation/Foundation.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDIMapping;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  A parser for XML MIDI mapping files. Only used on iOS. On OS X, NSXMLDocument is used
  *  directly instead. Should be considered "private" for use by MIKMIDIMapping.
@@ -22,3 +25,5 @@
 @property (nonatomic, strong, readonly) NSArray *mappings;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMappingXMLParser.m b/Source/MIKMIDIMappingXMLParser.m
index 5be67ef6..29daa56a 100644
--- a/Source/MIKMIDIMappingXMLParser.m
+++ b/Source/MIKMIDIMappingXMLParser.m
@@ -42,7 +42,9 @@ + (instancetype)parserWithXMLData:(NSData *)xmlData
 
 - (instancetype)initWithXMLData:(NSData *)xmlData
 {
-	if (![xmlData length]) return nil;
+	if (![xmlData length]) {
+		[NSException raise:NSInvalidArgumentException format:"Argument passed to -[%@ %@] must have a non-zero length.", NSStringFromClass([self class]), NSStringFromSelector(_cmd)];
+	}
 	
 	self = [super init];
 	if (self) {
@@ -160,7 +162,7 @@ - (void)parserDidEndDocument:(NSXMLParser *)parser
 - (NSArray *)mappings
 {
 	if (!self.hasParsed) [self parse];
-	return _mappings;
+	return _mappings ?: @[];
 }
 
 @end
diff --git a/Source/MIKMIDIMetaCopyrightEvent.h b/Source/MIKMIDIMetaCopyrightEvent.h
index 36de74e5..b096106e 100644
--- a/Source/MIKMIDIMetaCopyrightEvent.h
+++ b/Source/MIKMIDIMetaCopyrightEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIMetaTextEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A meta event containing copyright information.
@@ -22,6 +25,8 @@
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 @property (nonatomic, readwrite) UInt8 metadataType;
-@property (nonatomic, strong, readwrite) NSData *metaData;
+@property (nonatomic, strong, readwrite, null_resettable) NSData *metaData;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMetaCuePointEvent.h b/Source/MIKMIDIMetaCuePointEvent.h
index f9861002..d2de0268 100644
--- a/Source/MIKMIDIMetaCuePointEvent.h
+++ b/Source/MIKMIDIMetaCuePointEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIMetaTextEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A meta event containing cue point information.
@@ -22,6 +25,8 @@
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 @property (nonatomic, readwrite) UInt8 metadataType;
-@property (nonatomic, strong, readwrite) NSData *metaData;
+@property (nonatomic, strong, readwrite, null_resettable) NSData *metaData;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMetaEvent.h b/Source/MIKMIDIMetaEvent.h
index b931ad77..d7edec4c 100644
--- a/Source/MIKMIDIMetaEvent.h
+++ b/Source/MIKMIDIMetaEvent.h
@@ -7,9 +7,12 @@
 //
 
 #import "MIKMIDIEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
 
 #define MIKMIDIEventMetadataStartOffset 8
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  A MIDI meta event.
  */
@@ -40,6 +43,8 @@
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 @property (nonatomic, readwrite) UInt8 metadataType;
-@property (nonatomic, strong, readwrite) NSData *metaData;
+@property (nonatomic, strong, readwrite, null_resettable) NSData *metaData;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMetaEvent.m b/Source/MIKMIDIMetaEvent.m
index 0e96286d..c3e56060 100644
--- a/Source/MIKMIDIMetaEvent.m
+++ b/Source/MIKMIDIMetaEvent.m
@@ -73,7 +73,7 @@ - (void)setMetaData:(NSData *)metaData
     metaEvent->dataLength = (UInt32)[metaData length];
     NSMutableData *newMetaData = [[self.internalData subdataWithRange:NSMakeRange(0, MIKMIDIEventMetadataStartOffset)] mutableCopy];
     [newMetaData appendData:metaData];
-    self.internalData = newMetaData;
+	self.internalData = newMetaData ?: [NSMutableData data];
 }
 
 @end
diff --git a/Source/MIKMIDIMetaEvent_SubclassMethods.h b/Source/MIKMIDIMetaEvent_SubclassMethods.h
new file mode 100644
index 00000000..fb9998e8
--- /dev/null
+++ b/Source/MIKMIDIMetaEvent_SubclassMethods.h
@@ -0,0 +1,16 @@
+//
+//  MIKMIDIMetaEvent_SubclassMethods.h
+//  MIKMIDI
+//
+//  Created by Andrew Madsen on 11/10/15.
+//  Copyright © 2015 Mixed In Key. All rights reserved.
+//
+
+#import <MIKMIDI/MIKMIDI.h>
+#import "MIKMIDIEvent_SubclassMethods.h"
+
+@interface MIKMIDIMetaEvent ()
+
+@property (nonatomic, strong, readwrite) NSData *metaData;
+
+@end
diff --git a/Source/MIKMIDIMetaInstrumentNameEvent.h b/Source/MIKMIDIMetaInstrumentNameEvent.h
index 34aac8bf..276a912b 100644
--- a/Source/MIKMIDIMetaInstrumentNameEvent.h
+++ b/Source/MIKMIDIMetaInstrumentNameEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIMetaTextEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A meta event containing an instrument name.
@@ -23,6 +26,8 @@
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 @property (nonatomic, readwrite) UInt8 metadataType;
-@property (nonatomic, strong, readwrite) NSData *metaData;
+@property (nonatomic, strong, readwrite, null_resettable) NSData *metaData;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMetaKeySignatureEvent.h b/Source/MIKMIDIMetaKeySignatureEvent.h
index 3d004e9b..56b94107 100644
--- a/Source/MIKMIDIMetaKeySignatureEvent.h
+++ b/Source/MIKMIDIMetaKeySignatureEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIMetaEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A meta event containing key signature information.
@@ -33,8 +36,10 @@
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 @property (nonatomic, readwrite) UInt8 metadataType;
-@property (nonatomic, strong, readwrite) NSData *metaData;
+@property (nonatomic, strong, readwrite, null_resettable) NSData *metaData;
 @property (nonatomic, readwrite) UInt8 key;
 @property (nonatomic, readwrite) UInt8 scale;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMetaKeySignatureEvent.m b/Source/MIKMIDIMetaKeySignatureEvent.m
index 00303e7d..2b5e7f08 100644
--- a/Source/MIKMIDIMetaKeySignatureEvent.m
+++ b/Source/MIKMIDIMetaKeySignatureEvent.m
@@ -7,7 +7,7 @@
 //
 
 #import "MIKMIDIMetaKeySignatureEvent.h"
-#import "MIKMIDIEvent_SubclassMethods.h"
+#import "MIKMIDIMetaEvent_SubclassMethods.h"
 #import "MIKMIDIUtilities.h"
 
 #if !__has_feature(objc_arc)
diff --git a/Source/MIKMIDIMetaLyricEvent.h b/Source/MIKMIDIMetaLyricEvent.h
index d19bcfef..ae3fe3cb 100644
--- a/Source/MIKMIDIMetaLyricEvent.h
+++ b/Source/MIKMIDIMetaLyricEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIMetaTextEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A meta event containing lyrics.
@@ -22,6 +25,8 @@
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 @property (nonatomic, readwrite) UInt8 metadataType;
-@property (nonatomic, strong, readwrite) NSData *metaData;
+@property (nonatomic, strong, readwrite, null_resettable) NSData *metaData;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMetaMarkerTextEvent.h b/Source/MIKMIDIMetaMarkerTextEvent.h
index 358a9132..2a47a757 100644
--- a/Source/MIKMIDIMetaMarkerTextEvent.h
+++ b/Source/MIKMIDIMetaMarkerTextEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIMetaTextEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A meta event containing marker information.
@@ -22,6 +25,8 @@
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 @property (nonatomic, readwrite) UInt8 metadataType;
-@property (nonatomic, strong, readwrite) NSData *metaData;
+@property (nonatomic, strong, readwrite, null_resettable) NSData *metaData;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMetaSequenceEvent.h b/Source/MIKMIDIMetaSequenceEvent.h
index e2aa1f3f..2ea9b8e2 100644
--- a/Source/MIKMIDIMetaSequenceEvent.h
+++ b/Source/MIKMIDIMetaSequenceEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIMetaEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A meta event containing sequence information.
@@ -22,6 +25,8 @@
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 @property (nonatomic, readwrite) UInt8 metadataType;
-@property (nonatomic, strong, readwrite) NSData *metaData;
+@property (nonatomic, strong, readwrite, null_resettable) NSData *metaData;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMetaTextEvent.h b/Source/MIKMIDIMetaTextEvent.h
index 271de1b0..3c1db46a 100644
--- a/Source/MIKMIDIMetaTextEvent.h
+++ b/Source/MIKMIDIMetaTextEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIMetaEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A meta event containing text.
@@ -16,7 +19,7 @@
 /**
  *  The text for the event.
  */
-@property (nonatomic, readonly) NSString *string;
+@property (nonatomic, readonly, nullable) NSString *string;
 
 @end
 
@@ -27,7 +30,9 @@
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 @property (nonatomic, readwrite) UInt8 metadataType;
-@property (nonatomic, strong, readwrite) NSData *metaData;
-@property (nonatomic, copy, readwrite) NSString *string;
+@property (nonatomic, strong, readwrite, null_resettable) NSData *metaData;
+@property (nonatomic, copy, readwrite, nullable) NSString *string;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMetaTextEvent.m b/Source/MIKMIDIMetaTextEvent.m
index 2ff5d018..39c085fc 100644
--- a/Source/MIKMIDIMetaTextEvent.m
+++ b/Source/MIKMIDIMetaTextEvent.m
@@ -7,7 +7,7 @@
 //
 
 #import "MIKMIDIMetaTextEvent.h"
-#import "MIKMIDIEvent_SubclassMethods.h"
+#import "MIKMIDIMetaEvent_SubclassMethods.h"
 #import "MIKMIDIUtilities.h"
 
 #if !__has_feature(objc_arc)
diff --git a/Source/MIKMIDIMetaTimeSignatureEvent.h b/Source/MIKMIDIMetaTimeSignatureEvent.h
index 3810d182..a4692dd7 100644
--- a/Source/MIKMIDIMetaTimeSignatureEvent.h
+++ b/Source/MIKMIDIMetaTimeSignatureEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIMetaEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A meta event containing time signature information.
@@ -41,11 +44,13 @@
 @interface MIKMutableMIDIMetaTimeSignatureEvent : MIKMIDIMetaTimeSignatureEvent
 
 @property (nonatomic, readwrite) UInt8 metadataType;
-@property (nonatomic, strong, readwrite) NSData *metaData;
+@property (nonatomic, strong, readwrite, null_resettable) NSData *metaData;
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 @property (nonatomic, readwrite) UInt8 numerator;
 @property (nonatomic, readwrite) UInt8 denominator;
 @property (nonatomic, readwrite) UInt8 metronomePulse;
 @property (nonatomic, readwrite) UInt8 thirtySecondsPerQuarterNote;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMetaTimeSignatureEvent.m b/Source/MIKMIDIMetaTimeSignatureEvent.m
index c5561bae..16ff81ba 100644
--- a/Source/MIKMIDIMetaTimeSignatureEvent.m
+++ b/Source/MIKMIDIMetaTimeSignatureEvent.m
@@ -7,7 +7,7 @@
 //
 
 #import "MIKMIDIMetaTimeSignatureEvent.h"
-#import "MIKMIDIEvent_SubclassMethods.h"
+#import "MIKMIDIMetaEvent_SubclassMethods.h"
 #import "MIKMIDIUtilities.h"
 
 #if !__has_feature(objc_arc)
diff --git a/Source/MIKMIDIMetaTrackSequenceNameEvent.h b/Source/MIKMIDIMetaTrackSequenceNameEvent.h
index 42883361..a037792a 100644
--- a/Source/MIKMIDIMetaTrackSequenceNameEvent.h
+++ b/Source/MIKMIDIMetaTrackSequenceNameEvent.h
@@ -7,13 +7,16 @@
 //
 
 #import "MIKMIDIMetaTextEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A meta event containing a track name.
  */
 @interface MIKMIDIMetaTrackSequenceNameEvent : MIKMIDIMetaTextEvent
 
-@property (nonatomic, readonly) NSString *name;
+@property (nonatomic, readonly, nullable) NSString *name;
 
 @end
 
@@ -22,11 +25,13 @@
  */
 @interface MIKMutableMIDIMetaTrackSequenceNameEvent : MIKMIDIMetaTrackSequenceNameEvent
 
-@property (nonatomic, copy, readwrite) NSString *name;
+@property (nonatomic, copy, readwrite, nullable) NSString *name;
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
 @property (nonatomic, readwrite) UInt8 metadataType;
-@property (nonatomic, strong, readwrite) NSData *metaData;
+@property (nonatomic, strong, readwrite, null_resettable) NSData *metaData;
 @property (nonatomic, copy, readwrite) NSString *string;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIMetronome.h b/Source/MIKMIDIMetronome.h
index 37a15072..4cebe7cf 100644
--- a/Source/MIKMIDIMetronome.h
+++ b/Source/MIKMIDIMetronome.h
@@ -7,7 +7,9 @@
 //
 
 #import "MIKMIDIEndpointSynthesizer.h"
+#import "MIKMIDICompilerCompatibility.h"
 
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *	This class is only a subclass of MIKMIDIEndpointSynthesizer so it continues to function with MIKMIDIPlayer while
@@ -29,4 +31,6 @@
  */
 - (BOOL)setupMetronome;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/Source/MIKMIDINoteEvent.h b/Source/MIKMIDINoteEvent.h
index 61986c7c..30aa6701 100644
--- a/Source/MIKMIDINoteEvent.h
+++ b/Source/MIKMIDINoteEvent.h
@@ -7,9 +7,12 @@
 //
 
 #import "MIKMIDIEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDIClock;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  A MIDI note event.
  */
@@ -26,11 +29,11 @@
  *
  *  @return An initialized MIKMIDINoteEvent instance, or nil if an error occurred.
  */
-+ (instancetype)noteEventWithTimeStamp:(MusicTimeStamp)timeStamp
-								  note:(UInt8)note
-							  velocity:(UInt8)velocity
-							  duration:(Float32)duration
-							   channel:(UInt8)channel;
++ (nullable instancetype)noteEventWithTimeStamp:(MusicTimeStamp)timeStamp
+										   note:(UInt8)note
+									   velocity:(UInt8)velocity
+									   duration:(Float32)duration
+										channel:(UInt8)channel;
 
 /**
  *  Convenience method for creating a new MIKMIDINoteEvent from a CoreMIDI MIDINoteMessage struct.
@@ -40,7 +43,7 @@
  *
  *  @return A new MIKMIDINoteEvent instance, or nil if there is an error.
  */
-+ (instancetype)noteEventWithTimeStamp:(MusicTimeStamp)timeStamp message:(MIDINoteMessage)message;
++ (nullable instancetype)noteEventWithTimeStamp:(MusicTimeStamp)timeStamp message:(MIDINoteMessage)message;
 
 // Properties
 
@@ -99,7 +102,7 @@
 @interface MIKMutableMIDINoteEvent : MIKMIDINoteEvent
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
-@property (nonatomic, strong, readwrite) NSMutableData *data;
+@property (nonatomic, strong, readwrite, null_resettable) NSMutableData *data;
 @property (nonatomic, readwrite) UInt8 note;
 @property (nonatomic, readwrite) UInt8 velocity;
 @property (nonatomic, readwrite) UInt8 channel;
@@ -108,15 +111,21 @@
 
 @end
 
+NS_ASSUME_NONNULL_END
+
 #pragma mark -
 
 #import <MIKMIDI/MIKMIDINoteOnCommand.h>
 #import <MIKMIDI/MIKMIDINoteOffCommand.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface MIKMIDICommand (MIKMIDINoteEventToCommands)
 
 + (NSArray *)commandsFromNoteEvent:(MIKMIDINoteEvent *)noteEvent clock:(MIKMIDIClock *)clock;
 + (MIKMIDINoteOnCommand *)noteOnCommandFromNoteEvent:(MIKMIDINoteEvent *)noteEvent clock:(MIKMIDIClock *)clock;
 + (MIKMIDINoteOffCommand *)noteOffCommandFromNoteEvent:(MIKMIDINoteEvent *)noteEvent clock:(MIKMIDIClock *)clock;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDINoteOffCommand.h b/Source/MIKMIDINoteOffCommand.h
index 869dd567..1685a9ee 100644
--- a/Source/MIKMIDINoteOffCommand.h
+++ b/Source/MIKMIDINoteOffCommand.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIChannelVoiceCommand.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A MIDI note off message.
@@ -26,7 +29,7 @@
 + (instancetype)noteOffCommandWithNote:(NSUInteger)note
 							  velocity:(NSUInteger)velocity
 							   channel:(UInt8)channel
-							 timestamp:(NSDate *)timestamp;
+							 timestamp:(nullable NSDate *)timestamp;
 
 /**
  *  The note number for the message. In the range 0-127.
@@ -53,4 +56,6 @@
 @property (nonatomic, readwrite) NSUInteger note;
 @property (nonatomic, readwrite) NSUInteger velocity;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDINoteOnCommand.h b/Source/MIKMIDINoteOnCommand.h
index b7f023b6..2ef9aae1 100644
--- a/Source/MIKMIDINoteOnCommand.h
+++ b/Source/MIKMIDINoteOnCommand.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIChannelVoiceCommand.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A MIDI note on message.
@@ -26,7 +29,7 @@
 + (instancetype)noteOnCommandWithNote:(NSUInteger)note
 							 velocity:(NSUInteger)velocity
 							  channel:(UInt8)channel
-							timestamp:(NSDate *)timestamp;
+							timestamp:(nullable NSDate *)timestamp;
 
 /**
  *  The note number for the message. In the range 0-127.
@@ -54,3 +57,5 @@
 @property (nonatomic, readwrite) NSUInteger velocity;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIObject_SubclassMethods.h b/Source/MIKMIDIObject_SubclassMethods.h
index 1e3544d3..bbf9c60c 100644
--- a/Source/MIKMIDIObject_SubclassMethods.h
+++ b/Source/MIKMIDIObject_SubclassMethods.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIObject.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  These methods can be called and/or overridden by subclasses of MIKMIDIObject, but are not
@@ -55,3 +58,5 @@
 @property (nonatomic, readwrite) BOOL isVirtual;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIOutputPort.h b/Source/MIKMIDIOutputPort.h
index ee5c6d5a..0b4c740b 100644
--- a/Source/MIKMIDIOutputPort.h
+++ b/Source/MIKMIDIOutputPort.h
@@ -7,10 +7,13 @@
 //
 
 #import "MIKMIDIPort.h"
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDICommand;
 @class MIKMIDIDestinationEndpoint;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  MIKMIDIOutputPort is an Objective-C wrapper for CoreMIDI's MIDIPort class, and is only for destination ports.
  *  It is not intended for use by clients/users of of MIKMIDI. Rather, it should be thought of as an
@@ -21,3 +24,5 @@
 - (BOOL)sendCommands:(NSArray *)commands toDestination:(MIKMIDIDestinationEndpoint *)destination error:(NSError **)error;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIOutputPort.m b/Source/MIKMIDIOutputPort.m
index 091af2c5..70f77ced 100644
--- a/Source/MIKMIDIOutputPort.m
+++ b/Source/MIKMIDIOutputPort.m
@@ -17,7 +17,7 @@
 
 @implementation MIKMIDIOutputPort
 
-- (id)initWithClient:(MIDIClientRef)clientRef name:(NSString *)name
+- (instancetype)initWithClient:(MIDIClientRef)clientRef name:(NSString *)name
 {
 	self = [super initWithClient:clientRef name:name];
 	if (self) {
diff --git a/Source/MIKMIDIPitchBendChangeCommand.h b/Source/MIKMIDIPitchBendChangeCommand.h
index 758e62cd..65bda0a0 100644
--- a/Source/MIKMIDIPitchBendChangeCommand.h
+++ b/Source/MIKMIDIPitchBendChangeCommand.h
@@ -7,6 +7,9 @@
 //
 
 #import <MIKMIDI/MIKMIDIChannelVoiceCommand.h>
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A MIDI pitch bend change command.
@@ -37,6 +40,8 @@
 @property (nonatomic, readwrite) UInt8 dataByte2;
 
 @property (nonatomic, readwrite) MIDITimeStamp midiTimestamp;
-@property (nonatomic, copy, readwrite) NSData *data;
+@property (nonatomic, copy, readwrite, null_resettable) NSData *data;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIPitchBendChangeEvent.h b/Source/MIKMIDIPitchBendChangeEvent.h
index 36db4e01..2c84e07f 100644
--- a/Source/MIKMIDIPitchBendChangeEvent.h
+++ b/Source/MIKMIDIPitchBendChangeEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIChannelEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A pitch bed change event.
@@ -33,9 +36,11 @@
 @property (nonatomic, readonly) UInt16 pitchChange;
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
-@property (nonatomic, strong, readwrite) NSMutableData *data;
+@property (nonatomic, strong, readwrite, null_resettable) NSMutableData *data;
 @property (nonatomic, readwrite) UInt8 channel;
 @property (nonatomic, readwrite) UInt8 dataByte1;
 @property (nonatomic, readwrite) UInt8 dataByte2;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIPlayer.h b/Source/MIKMIDIPlayer.h
index b6c5a257..79b08225 100644
--- a/Source/MIKMIDIPlayer.h
+++ b/Source/MIKMIDIPlayer.h
@@ -8,10 +8,13 @@
 
 #import <Foundation/Foundation.h>
 #import <AudioToolbox/AudioToolbox.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDISequence;
 @class MIKMIDIMetronome;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  MIKMIDIPlayer can be used to play an MIKMIDISequence.
  */
@@ -53,7 +56,7 @@ __attribute((deprecated("use MIKMIDISequencer instead")))
 /**
  *  The music sequence to play.
  */
-@property (strong, nonatomic) MIKMIDISequence *sequence;
+@property (strong, nonatomic, nullable) MIKMIDISequence *sequence;
 
 /**
  *  The current position in the music sequence.
@@ -80,10 +83,12 @@ __attribute((deprecated("use MIKMIDISequencer instead")))
 @property (nonatomic, getter=isLooping) BOOL looping;
 
 @property (nonatomic, getter=isClickTrackEnabled) BOOL clickTrackEnabled;
-@property (strong, nonatomic) MIKMIDIMetronome *metronome;
+@property (strong, nonatomic, nullable) MIKMIDIMetronome *metronome;
 
 @property (nonatomic) BOOL stopPlaybackAtEndOfSequence;
 
 @property (nonatomic) MusicTimeStamp maxClickTrackTimeStamp;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/Source/MIKMIDIPolyphonicKeyPressureEvent.h b/Source/MIKMIDIPolyphonicKeyPressureEvent.h
index 58c78275..132317da 100644
--- a/Source/MIKMIDIPolyphonicKeyPressureEvent.h
+++ b/Source/MIKMIDIPolyphonicKeyPressureEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIChannelEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A polyphonic key pressure (aftertouch) event.
@@ -36,9 +39,11 @@
 @property (nonatomic, readwrite) UInt8 pressure;
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
-@property (nonatomic, strong, readwrite) NSMutableData *data;
+@property (nonatomic, strong, readwrite, null_resettable) NSMutableData *data;
 @property (nonatomic, readwrite) UInt8 channel;
 @property (nonatomic, readwrite) UInt8 dataByte1;
 @property (nonatomic, readwrite) UInt8 dataByte2;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIPort.h b/Source/MIKMIDIPort.h
index 081af502..e1cc52bb 100644
--- a/Source/MIKMIDIPort.h
+++ b/Source/MIKMIDIPort.h
@@ -8,17 +8,22 @@
 
 #import "MIKMIDIObject.h"
 #import <CoreMIDI/CoreMIDI.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDIEndpoint;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  MIKMIDIPort is an Objective-C wrapper for CoreMIDI's MIDIPort class. It is not intended for use by clients/users of
  *  of MIKMIDI. Rather, it should be thought of as an MIKMIDI private class.
  */
 @interface MIKMIDIPort : NSObject
 
-- (id)initWithClient:(MIDIClientRef)clientRef name:(NSString *)name;
+- (nullable instancetype)initWithClient:(MIDIClientRef)clientRef name:(NSString *)name;
 
 @property (nonatomic, readonly) MIDIPortRef portRef;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIPort.m b/Source/MIKMIDIPort.m
index 484ec886..b9a91bec 100644
--- a/Source/MIKMIDIPort.m
+++ b/Source/MIKMIDIPort.m
@@ -16,7 +16,7 @@
 
 @implementation MIKMIDIPort
 
-- (id)initWithClient:(MIDIClientRef)clientRef name:(NSString *)name
+- (instancetype)initWithClient:(MIDIClientRef)clientRef name:(NSString *)name
 {
 	self = [super init];
 	if (self) {
diff --git a/Source/MIKMIDIPort_SubclassMethods.h b/Source/MIKMIDIPort_SubclassMethods.h
index 9ef4fd05..282bfe10 100644
--- a/Source/MIKMIDIPort_SubclassMethods.h
+++ b/Source/MIKMIDIPort_SubclassMethods.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIPort.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 @interface MIKMIDIPort ()
 
@@ -14,3 +17,4 @@
 
 @end
 
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIPrivateUtilities.h b/Source/MIKMIDIPrivateUtilities.h
index acf41de2..df1bf0ac 100644
--- a/Source/MIKMIDIPrivateUtilities.h
+++ b/Source/MIKMIDIPrivateUtilities.h
@@ -7,8 +7,13 @@
 //
 
 #import <Foundation/Foundation.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDIChannelVoiceCommand;
 
+NS_ASSUME_NONNULL_BEGIN
+
 NSUInteger MIKMIDIControlNumberFromCommand(MIKMIDIChannelVoiceCommand *command);
 float MIKMIDIControlValueFromChannelVoiceCommand(MIKMIDIChannelVoiceCommand *command);
+
+NS_ASSUME_NONNULL_END
diff --git a/Source/MIKMIDIProgramChangeCommand.h b/Source/MIKMIDIProgramChangeCommand.h
index 5a1aad29..032422cc 100644
--- a/Source/MIKMIDIProgramChangeCommand.h
+++ b/Source/MIKMIDIProgramChangeCommand.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIChannelVoiceCommand.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A MIDI program change message.
@@ -34,4 +37,6 @@
 
 @property (nonatomic, readwrite) NSUInteger programNumber;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIProgramChangeEvent.h b/Source/MIKMIDIProgramChangeEvent.h
index 2133b48c..10b5c35a 100644
--- a/Source/MIKMIDIProgramChangeEvent.h
+++ b/Source/MIKMIDIProgramChangeEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIChannelEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A MIDI program change event.
@@ -40,9 +43,11 @@
 @property (nonatomic, readwrite) NSUInteger programNumber;
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
-@property (nonatomic, strong, readwrite) NSMutableData *data;
+@property (nonatomic, strong, readwrite, null_resettable) NSMutableData *data;
 @property (nonatomic, readwrite) UInt8 channel;
 @property (nonatomic, readwrite) UInt8 dataByte1;
 @property (nonatomic, readwrite) UInt8 dataByte2;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDIResponder.h b/Source/MIKMIDIResponder.h
index be091319..4cba7517 100644
--- a/Source/MIKMIDIResponder.h
+++ b/Source/MIKMIDIResponder.h
@@ -7,9 +7,12 @@
 //
 
 #import <Foundation/Foundation.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDICommand;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  The MIKMIDIResponder protocol defines methods to be implemented by any object that wishes
  *  to receive MIDI messages/commands.
@@ -63,11 +66,13 @@
  *  application, as long as the receiver (or a parent responder) is registered.
  *
  *  Should return a flat (non-recursive) array of subresponders.
- *  Return nil, empty array, or don't implement if you don't want subresponders to be
+ *  Return empty array, or don't implement if you don't want subresponders to be
  *  included in any case where the receiver would be considered for receiving MIDI
  *
  *  @return An NSArray containing the receivers subresponders. Each object in the array must also conform to MIKMIDIResponder.
  */
-- (NSArray *)subresponders;
+- (nullable NSArray *)subresponders; // Nullable for historical reasons.
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDISequence+MIKMIDIPrivate.h b/Source/MIKMIDISequence+MIKMIDIPrivate.h
index 1e4333da..a3da04c5 100644
--- a/Source/MIKMIDISequence+MIKMIDIPrivate.h
+++ b/Source/MIKMIDISequence+MIKMIDIPrivate.h
@@ -7,12 +7,16 @@
 //
 
 #import <MIKMIDI/MIKMIDI.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDISequencer;
 
+NS_ASSUME_NONNULL_BEGIN
 
 @interface MIKMIDISequence (MIKMIDIPrivate)
 
-@property (weak, nonatomic) MIKMIDISequencer *sequencer;
+@property (weak, nonatomic, nullable) MIKMIDISequencer *sequencer;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDISequence.h b/Source/MIKMIDISequence.h
index 5a45258a..420edf1e 100644
--- a/Source/MIKMIDISequence.h
+++ b/Source/MIKMIDISequence.h
@@ -8,7 +8,7 @@
 
 #import <Foundation/Foundation.h>
 #import <AudioToolbox/AudioToolbox.h>
-
+#import "MIKMIDICompilerCompatibility.h"
 
 typedef struct {
 	UInt8 numerator;
@@ -26,6 +26,8 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
 @class MIKMIDISequencer;
 @class MIKMIDIDestinationEndpoint;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  Instances of MIKMIDISequence contain a collection of MIDI tracks. MIKMIDISequences may be thought
  *  of as MIDI "songs". They can be loaded from and saved to MIDI files. They can also be played
@@ -41,7 +43,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *
  *  @return A new instance of MIKMIDISequence, or nil if an error occured.
  */
-+ (instancetype)sequence;
++ (nullable instancetype)sequence;
 
 /**
  *  Creates and initilazes a new instance of MIKMIDISequence from a MIDI file.
@@ -52,7 +54,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *
  *  @return A new instance of MIKMIDISequence containing the loaded file's MIDI sequence, or nil if an error occured.
  */
-+ (instancetype)sequenceWithFileAtURL:(NSURL *)fileURL error:(NSError **)error;
++ (nullable instancetype)sequenceWithFileAtURL:(NSURL *)fileURL error:(NSError **)error;
 
 /**
  *  Creates and initilazes a new instance of MIKMIDISequence from a MIDI file.
@@ -66,7 +68,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *
  *  @return A new instance of MIKMIDISequence containing the loaded file's MIDI sequence, or nil if an error occured.
  */
-+ (instancetype)sequenceWithFileAtURL:(NSURL *)fileURL convertMIDIChannelsToTracks:(BOOL)convertMIDIChannelsToTracks error:(NSError **)error;
++ (nullable instancetype)sequenceWithFileAtURL:(NSURL *)fileURL convertMIDIChannelsToTracks:(BOOL)convertMIDIChannelsToTracks error:(NSError **)error;
 
 /**
  *  Initilazes a new instance of MIKMIDISequence from a MIDI file.
@@ -77,7 +79,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *
  *  @return A new instance of MIKMIDISequence containing the loaded file's MIDI sequence, or nil if an error occured.
  */
-- (instancetype)initWithFileAtURL:(NSURL *)fileURL error:(NSError **)error;
+- (nullable instancetype)initWithFileAtURL:(NSURL *)fileURL error:(NSError **)error;
 
 /**
  *  Initilazes a new instance of MIKMIDISequence from a MIDI file.
@@ -91,7 +93,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *
  *  @return A new instance of MIKMIDISequence containing the loaded file's MIDI sequence, or nil if an error occured.
  */
-- (instancetype)initWithFileAtURL:(NSURL *)fileURL convertMIDIChannelsToTracks:(BOOL)convertMIDIChannelsToTracks error:(NSError **)error;
+- (nullable instancetype)initWithFileAtURL:(NSURL *)fileURL convertMIDIChannelsToTracks:(BOOL)convertMIDIChannelsToTracks error:(NSError **)error;
 
 /**
  *  Creates and initializes a new instance of MIKMIDISequence from MIDI data.
@@ -102,7 +104,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *  @return If an error occurs, upon return contains an NSError object that describes the problem. If you are not interested in possible errors,
  *  you may pass in NULL.
  */
-+ (instancetype)sequenceWithData:(NSData *)data error:(NSError **)error;
++ (nullable instancetype)sequenceWithData:(NSData *)data error:(NSError **)error;
 
 /**
  *  Creates and initializes a new instance of MIKMIDISequence from MIDI data.
@@ -116,7 +118,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *  @return If an error occurs, upon return contains an NSError object that describes the problem. If you are not interested in possible errors,
  *  you may pass in NULL.
  */
-+ (instancetype)sequenceWithData:(NSData *)data convertMIDIChannelsToTracks:(BOOL)convertMIDIChannelsToTracks error:(NSError **)error;
++ (nullable instancetype)sequenceWithData:(NSData *)data convertMIDIChannelsToTracks:(BOOL)convertMIDIChannelsToTracks error:(NSError **)error;
 
 /**
  *  Initializes a new instance of MIKMIDISequence from MIDI data.
@@ -127,7 +129,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *  @return If an error occurs, upon return contains an NSError object that describes the problem. If you are not interested in possible errors,
  *  you may pass in NULL.
  */
-- (instancetype)initWithData:(NSData *)data error:(NSError **)error;
+- (nullable instancetype)initWithData:(NSData *)data error:(NSError **)error;
 
 /**
  *  Initializes a new instance of MIKMIDISequence from MIDI data.
@@ -141,7 +143,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *  @return If an error occurs, upon return contains an NSError object that describes the problem. If you are not interested in possible errors,
  *  you may pass in NULL.
  */
-- (instancetype)initWithData:(NSData *)data convertMIDIChannelsToTracks:(BOOL)convertMIDIChannelsToTracks error:(NSError **)error;
+- (nullable instancetype)initWithData:(NSData *)data convertMIDIChannelsToTracks:(BOOL)convertMIDIChannelsToTracks error:(NSError **)error;
 
 /**
  *  Writes the MIDI sequence in Standard MIDI File format to a file at the specified URL.
@@ -157,9 +159,9 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
 #pragma mark - Track Management
 
 /**
- *  Creates and adds a new MIDI track to the sequence.
+ *  Creates and adds a new MIDI track to the sequence. May return nil if an error occurs.
  */
-- (MIKMIDITrack *)addTrack;
+- (nullable MIKMIDITrack *)addTrack;
 
 /**
  *  Removes the specified MIDI track from the sequence.
@@ -271,7 +273,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
 /**
  *	The sequencer this sequence is assigned to for playback.
  */
-@property (nonatomic, readonly) MIKMIDISequencer *sequencer;
+@property (nonatomic, readonly, nullable) MIKMIDISequencer *sequencer;
 
 /**
  *  The tempo track for the sequence. Even in a new, empty sequence,
@@ -311,7 +313,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
 /**
  *  The MIDI data that composes the sequence. This data is equivalent to an NSData representation of a standard MIDI file.
  */
-@property (nonatomic, readonly) NSData *dataValue;
+@property (nonatomic, readonly, nullable) NSData *dataValue;
 
 /**
  *  A block to be called for each user event added to any music track owned by the sequence.
@@ -332,7 +334,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *
  *  @return A new instance of MIKMIDISequence containing the MIDI data, or nil if an error occured.
  */
-+ (instancetype)sequenceWithData:(NSData *)data DEPRECATED_ATTRIBUTE;
++ (nullable instancetype)sequenceWithData:(NSData *)data DEPRECATED_ATTRIBUTE;
 
 /**
  *  @deprecated This method is deprecated. Use -initWithData:error: instead.
@@ -343,7 +345,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *
  *  @return A new instance of MIKMIDISequence containing the MIDI data, or nil if an error occured.
  */
-- (instancetype)initWithData:(NSData *)data DEPRECATED_ATTRIBUTE;
+- (nullable instancetype)initWithData:(NSData *)data DEPRECATED_ATTRIBUTE;
 
 /**
  *	@deprecated This method is deprecated. Use -[MIKMIDISequencer 
@@ -353,7 +355,7 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
  *
  *  @param destinationEndpoint The destination endpoint to set for each track in the sequence.
  */
-- (void)setDestinationEndpoint:(MIKMIDIDestinationEndpoint *)destinationEndpoint DEPRECATED_ATTRIBUTE;
+- (void)setDestinationEndpoint:(nullable MIKMIDIDestinationEndpoint *)destinationEndpoint DEPRECATED_ATTRIBUTE;
 
 /**
  *	@deprecated This method has been replaced by -tempoAtTimeStamp: and simply calls through to that method.
@@ -393,5 +395,6 @@ NS_INLINE MIKMIDITimeSignature MIKMIDITimeSignatureMake(UInt8 numerator, UInt8 d
 
 @end
 
-
 FOUNDATION_EXPORT const MusicTimeStamp MIKMIDISequenceLongestTrackLength;
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDISequence.m b/Source/MIKMIDISequence.m
index 09642772..6d7dfaee 100644
--- a/Source/MIKMIDISequence.m
+++ b/Source/MIKMIDISequence.m
@@ -174,7 +174,7 @@ - (void)dealloc
 {
 	NSArray *tracks = self.internalTracks;
 	self.internalTracks = nil; // Unregister for KVO
-    self.callBackBlock = nil;
+	[self setCallBackBlock:^(MIKMIDITrack *t, MusicTimeStamp ts, const MusicEventUserData *ud, MusicTimeStamp ts2, MusicTimeStamp ts3) {}];
 
 	for (MIKMIDITrack *track in tracks) {
 		OSStatus err = MusicSequenceDisposeTrack(_musicSequence, track.musicTrack);
@@ -208,7 +208,7 @@ - (MIKMIDITrack *)addTrack
 	[self dispatchSyncToSequencerProcessingQueueAsNeeded:^{
 		MusicTrack musicTrack;
 		OSStatus err = MusicSequenceNewTrack(self.musicSequence, &musicTrack);
-		if (err) return NSLog(@"MusicSequenceNewTrack() failed with error %@ in %s.", @(err), __PRETTY_FUNCTION__);
+		if (err) { NSLog(@"MusicSequenceNewTrack() failed with error %@ in %s.", @(err), __PRETTY_FUNCTION__); };
 
 		track = [MIKMIDITrack trackWithSequence:self musicTrack:musicTrack];
 		[self insertObject:track inInternalTracksAtIndex:[self.internalTracks count]];
@@ -434,7 +434,7 @@ - (NSArray *)tracks
 		tracks = self.internalTracks;
 	}];
 
-	return tracks;
+	return tracks ?: @[];
 }
 
 + (NSSet *)keyPathsForValuesAffectingLength
diff --git a/Source/MIKMIDISequencer+MIKMIDIPrivate.h b/Source/MIKMIDISequencer+MIKMIDIPrivate.h
index f5880b74..4cea3251 100644
--- a/Source/MIKMIDISequencer+MIKMIDIPrivate.h
+++ b/Source/MIKMIDISequencer+MIKMIDIPrivate.h
@@ -7,10 +7,14 @@
 //
 
 #import <MIKMIDI/MIKMIDI.h>
+#import "MIKMIDICompilerCompatibility.h"
 
+NS_ASSUME_NONNULL_BEGIN
 
 @interface MIKMIDISequencer (MIKMIDIPrivate)
 
 - (void)dispatchSyncToProcessingQueueAsNeeded:(void (^)())block;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDISequencer.h b/Source/MIKMIDISequencer.h
index 81143e81..ff150551 100644
--- a/Source/MIKMIDISequencer.h
+++ b/Source/MIKMIDISequencer.h
@@ -8,6 +8,7 @@
 
 #import <Foundation/Foundation.h>
 #import <AudioToolbox/AudioToolbox.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDISequence;
 @class MIKMIDITrack;
@@ -34,6 +35,7 @@ typedef NS_ENUM(NSInteger, MIKMIDISequencerClickTrackStatus) {
 	MIKMIDISequencerClickTrackStatusAlwaysEnabled
 };
 
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  MIKMIDISequencer can be used to play and record to an MIKMIDISequence.
@@ -205,10 +207,10 @@ typedef NS_ENUM(NSInteger, MIKMIDISequencerClickTrackStatus) {
  *  @note If track is not contained by the receiver's sequence, this method does nothing.
  *
  *  @param commandScheduler	An object that conforms to MIKMIDICommandScheduler with which events
- *	in track should be scheduled during playback.
+ *	in track should be scheduled during playback. Pass nil to remove an existing command scheduler
  *  @param track	An MIKMIDITrack instance.
  */
-- (void)setCommandScheduler:(id<MIKMIDICommandScheduler>)commandScheduler forTrack:(MIKMIDITrack *)track;
+- (void)setCommandScheduler:(nullable id<MIKMIDICommandScheduler>)commandScheduler forTrack:(MIKMIDITrack *)track;
 
 /**
  *  Returns the command scheduler for a track in the sequencer's sequence.
@@ -228,7 +230,7 @@ typedef NS_ENUM(NSInteger, MIKMIDISequencerClickTrackStatus) {
  *  @see -builtinSynthesizerForTrack:
  *	@see createSynthsIfNeeded
  */
-- (id<MIKMIDICommandScheduler>)commandSchedulerForTrack:(MIKMIDITrack *)track;
+- (nullable id<MIKMIDICommandScheduler>)commandSchedulerForTrack:(MIKMIDITrack *)track;
 
 /**
  *  Returns synthesizer the receiver will use to synthesize MIDI during playback
@@ -243,14 +245,14 @@ typedef NS_ENUM(NSInteger, MIKMIDISequencerClickTrackStatus) {
  *
  *  @return An MIKMIDISynthesizer instance, or nil if a builtin synthesizer for track doesn't exist.
  */
-- (MIKMIDISynthesizer *)builtinSynthesizerForTrack:(MIKMIDITrack *)track;
+- (nullable MIKMIDISynthesizer *)builtinSynthesizerForTrack:(MIKMIDITrack *)track;
 
 #pragma mark - Properties
 
 /**
  *  The sequence to playback and record to.
  */
-@property (strong, nonatomic) MIKMIDISequence *sequence;
+@property (nonatomic, strong) MIKMIDISequence *sequence;
 
 /**
  *	Whether or not the sequencer is currently playing. This can be observed with KVO.
@@ -371,7 +373,7 @@ typedef NS_ENUM(NSInteger, MIKMIDISequencerClickTrackStatus) {
 /**
  *  The metronome to send click track events to.
  */
-@property (strong, nonatomic) MIKMIDIMetronome *metronome;
+@property (nonatomic, strong, nullable) MIKMIDIMetronome *metronome;
 
 /**
  *  When the click track should be heard.
@@ -387,20 +389,20 @@ typedef NS_ENUM(NSInteger, MIKMIDISequencerClickTrackStatus) {
  *  @see recording
  *
  */
-@property (copy, nonatomic) NSSet *recordEnabledTracks;
+@property (nonatomic, copy, nullable) NSSet *recordEnabledTracks;
 
 /**
  *  An MIKMIDIClock that is synced with the sequencer's internal clock.
  *
  *  @  @see -[MIKMIDIClock syncedClock]
  */
-@property (readonly, nonatomic) MIKMIDIClock *syncedClock;
+@property (nonatomic, readonly) MIKMIDIClock *syncedClock;
 
 
 /**
  *  The latest MIDITimeStamp the sequencer has looked ahead to to schedule MIDI events.
  */
-@property (readonly, nonatomic) MIDITimeStamp latestScheduledMIDITimeStamp;
+@property (nonatomic, readonly) MIDITimeStamp latestScheduledMIDITimeStamp;
 
 #pragma mark - Deprecated
 
@@ -438,7 +440,7 @@ typedef NS_ENUM(NSInteger, MIKMIDISequencerClickTrackStatus) {
  *  @see -builtinSynthesizerForTrack:
  *	@see createSynthsAndEndpointsIfNeeded
  */
-- (MIKMIDIDestinationEndpoint *)destinationEndpointForTrack:(MIKMIDITrack *)track __attribute((deprecated("use -setCommandScheduler:forTrack: instead")));
+- (nullable MIKMIDIDestinationEndpoint *)destinationEndpointForTrack:(MIKMIDITrack *)track __attribute((deprecated("use -setCommandScheduler:forTrack: instead")));
 
 @end
 
@@ -453,3 +455,5 @@ FOUNDATION_EXPORT NSString * const MIKMIDISequencerWillLoopNotification;
  *	sequence regardless of sequence length.
  */
 FOUNDATION_EXPORT const MusicTimeStamp MIKMIDISequencerEndOfSequenceLoopEndTimeStamp;
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDISequencer.m b/Source/MIKMIDISequencer.m
index 67e9d00a..a74557dd 100644
--- a/Source/MIKMIDISequencer.m
+++ b/Source/MIKMIDISequencer.m
@@ -137,7 +137,7 @@ + (instancetype)sequencer
 
 - (void)dealloc
 {
-	self.sequence = nil;	// remove KVO
+	[_sequence removeObserver:self forKeyPath:@"tracks"];
 	self.processingTimer = NULL;
 }
 
@@ -552,6 +552,10 @@ - (MIKMIDINoteEvent	*)pendingNoteEventWithNoteNumber:(NSNumber *)noteNumber chan
 
 - (void)setCommandScheduler:(id<MIKMIDICommandScheduler>)commandScheduler forTrack:(MIKMIDITrack *)track
 {
+	if (!commandScheduler) {
+		[self.tracksToDestinationsMap removeObjectForKey:track];
+		return;
+	}
 	[self.tracksToDestinationsMap setObject:commandScheduler forKey:track];
 	[self.tracksToDefaultSynthsMap removeObjectForKey:track];
 }
diff --git a/Source/MIKMIDISourceEndpoint.h b/Source/MIKMIDISourceEndpoint.h
index cdb8a804..5a09251a 100644
--- a/Source/MIKMIDISourceEndpoint.h
+++ b/Source/MIKMIDISourceEndpoint.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIEndpoint.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  MIKMIDISourceEndpoint represents a source (input) MIDI endpoint.
@@ -26,3 +29,5 @@
 @interface MIKMIDISourceEndpoint : MIKMIDIEndpoint
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDISynthesizer.h b/Source/MIKMIDISynthesizer.h
index 9cdb4716..950fa537 100644
--- a/Source/MIKMIDISynthesizer.h
+++ b/Source/MIKMIDISynthesizer.h
@@ -10,6 +10,9 @@
 #import <AudioToolbox/AudioToolbox.h>
 #import "MIKMIDISynthesizerInstrument.h"
 #import "MIKMIDICommandScheduler.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  MIKMIDISynthesizer provides a simple way to synthesize MIDI messages to
@@ -35,7 +38,7 @@
  *
  *  @return An initialized MIKMIDIEndpointSynthesizer or nil if an error occurs.
  */
-- (instancetype)init;
+- (nullable instancetype)init;
 
 /**
  *  Initializes an MIKMIDISynthesizer instance which uses an audio unit matching
@@ -46,7 +49,7 @@
  *
  *  @return An initialized MIKMIDIEndpointSynthesizer or nil if an error occurs.
  */
-- (instancetype)initWithAudioUnitDescription:(AudioComponentDescription)componentDescription NS_DESIGNATED_INITIALIZER;
+- (nullable instancetype)initWithAudioUnitDescription:(AudioComponentDescription)componentDescription NS_DESIGNATED_INITIALIZER;
 
 /**
  *  This synthesizer's available instruments. An array of 
@@ -128,7 +131,7 @@
  *
  *  @see -setupAUGraph
  */
-@property (nonatomic, readonly) AudioUnit instrumentUnit;
+@property (nonatomic, readonly, nullable) AudioUnit instrumentUnit;
 
 /**
  *  The AUGraph for the instrument.
@@ -138,7 +141,7 @@
  *
  *  @see -setupAUGraph
  */
-@property (nonatomic) AUGraph graph;
+@property (nonatomic, nullable) AUGraph graph;
 
 // Deprecated
 
@@ -148,3 +151,5 @@
 @property (nonatomic) AudioUnit instrument DEPRECATED_ATTRIBUTE;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDISynthesizer.m b/Source/MIKMIDISynthesizer.m
index 8a2ec338..c784fcc9 100644
--- a/Source/MIKMIDISynthesizer.m
+++ b/Source/MIKMIDISynthesizer.m
@@ -98,7 +98,7 @@ - (NSArray *)availableInstruments
 			OSStatus err = AudioUnitGetProperty(audioUnit, kMusicDeviceProperty_InstrumentName, kAudioUnitScope_Global, instrumentID, &cName, &cNameSize);
 			if (err) {
 				NSLog(@"AudioUnitGetProperty() failed with error %@ in %s.", @(err), __PRETTY_FUNCTION__);
-				return nil;
+				return @[];
 			}
 			
 			NSString *name = [NSString stringWithCString:cName encoding:NSASCIIStringEncoding];
diff --git a/Source/MIKMIDISynthesizerInstrument.h b/Source/MIKMIDISynthesizerInstrument.h
index dd9abb51..216f4b8e 100644
--- a/Source/MIKMIDISynthesizerInstrument.h
+++ b/Source/MIKMIDISynthesizerInstrument.h
@@ -8,6 +8,9 @@
 
 #import <Foundation/Foundation.h>
 #import <AudioToolbox/AudioToolbox.h>
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  MIKMIDISynthesizerInstrument is used to represent
@@ -22,7 +25,7 @@
  *
  *  @return A MIKMIDISynthesizerInstrument instance with the matching instrument ID, or nil if no instrument was found.
  */
-+ (instancetype)instrumentWithID:(MusicDeviceInstrumentID)instrumentID name:(NSString *)name;
++ (nullable instancetype)instrumentWithID:(MusicDeviceInstrumentID)instrumentID name:(NSString *)name;
 
 /**
  *  The human readable name of the receiver. e.g. "Piano 1".
@@ -60,6 +63,8 @@
  *
  *  @return A MIKMIDISynthesizerInstrument with the matching instrument ID, or nil if no instrument was found.
  */
-+ (instancetype)instrumentWithID:(MusicDeviceInstrumentID)instrumentID DEPRECATED_ATTRIBUTE;
++ (nullable instancetype)instrumentWithID:(MusicDeviceInstrumentID)instrumentID DEPRECATED_ATTRIBUTE;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDISynthesizerInstrument.m b/Source/MIKMIDISynthesizerInstrument.m
index 0d5b2aca..b400ad39 100644
--- a/Source/MIKMIDISynthesizerInstrument.m
+++ b/Source/MIKMIDISynthesizerInstrument.m
@@ -19,7 +19,7 @@ - (instancetype)initWithName:(NSString *)name instrumentID:(MusicDeviceInstrumen
 {
 	self = [super init];
 	if (self) {
-		_name = name;
+		_name = name ?: @"No instrument name";
 		_instrumentID = instrumentID;
 	}
 	return self;
@@ -108,12 +108,12 @@ + (NSArray *)availableInstruments
 		availableInstruments = [result copy];
 	});
 	
-	return availableInstruments;
+	return availableInstruments ?: @[];
 }
 
 + (instancetype)instrumentWithID:(MusicDeviceInstrumentID)instrumentID
 {
-	return [self instrumentWithID:instrumentID name:nil];
+	return [self instrumentWithID:instrumentID name:@"Unspecified Name"];
 }
 
 @end
\ No newline at end of file
diff --git a/Source/MIKMIDISynthesizer_SubclassMethods.h b/Source/MIKMIDISynthesizer_SubclassMethods.h
index 6072a875..20990cc5 100644
--- a/Source/MIKMIDISynthesizer_SubclassMethods.h
+++ b/Source/MIKMIDISynthesizer_SubclassMethods.h
@@ -7,11 +7,16 @@
 //
 
 #import "MIKMIDISynthesizer.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 @interface MIKMIDISynthesizer ()
 
 - (BOOL)sendBankSelectAndProgramChangeForInstrumentID:(MusicDeviceInstrumentID)instrumentID error:(NSError **)error;
 
-@property (nonatomic, readwrite) AudioUnit instrumentUnit;
+@property (nonatomic, readwrite, nullable) AudioUnit instrumentUnit;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDISystemExclusiveCommand.h b/Source/MIKMIDISystemExclusiveCommand.h
index 09ccaa96..7e6e28d4 100644
--- a/Source/MIKMIDISystemExclusiveCommand.h
+++ b/Source/MIKMIDISystemExclusiveCommand.h
@@ -7,6 +7,7 @@
 //
 
 #import "MIKMIDISystemMessageCommand.h"
+#import "MIKMIDICompilerCompatibility.h"
 
 #define kMIKMIDISysexNonRealtimeManufacturerID 0x7E
 #define kMIKMIDISysexRealtimeManufacturerID 0x7F
@@ -14,6 +15,8 @@
 #define kMIKMIDISysexChannelDisregard 0x7F
 #define kMIKMIDISysexEndDelimiter 0xF7
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  A MIDI System Exclusive (SysEx) message. System exclusive messages are
  *  messages defined by individual manufacturers of MIDI devices. They
@@ -84,6 +87,8 @@
 @property (nonatomic, readwrite) UInt8 dataByte2;
 
 @property (nonatomic, readwrite) MIDITimeStamp midiTimestamp;
-@property (nonatomic, copy, readwrite) NSData *data;
+@property (nonatomic, copy, readwrite, null_resettable) NSData *data;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDISystemMessageCommand.h b/Source/MIKMIDISystemMessageCommand.h
index d3461512..7a537b84 100644
--- a/Source/MIKMIDISystemMessageCommand.h
+++ b/Source/MIKMIDISystemMessageCommand.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDICommand.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /**
  *  A MIDI system message command. This class is also the base class for
@@ -27,6 +30,8 @@
 @property (nonatomic, readwrite) UInt8 dataByte2;
 
 @property (nonatomic, readwrite) MIDITimeStamp midiTimestamp;
-@property (nonatomic, copy, readwrite) NSData *data;
+@property (nonatomic, copy, readwrite, null_resettable) NSData *data;
+
+@end
 
-@end
\ No newline at end of file
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDITempoEvent.h b/Source/MIKMIDITempoEvent.h
index d859a11d..61d23e8b 100644
--- a/Source/MIKMIDITempoEvent.h
+++ b/Source/MIKMIDITempoEvent.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDIEvent.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 /** 
  *  A MIDI tempo event.
@@ -22,7 +25,7 @@
  *
  *  @return A new instance of MIKMIDITempoEvent, or nil if an error occured.
  */
-+ (instancetype)tempoEventWithTimeStamp:(MusicTimeStamp)timeStamp tempo:(Float64)bpm;
++ (nullable instancetype)tempoEventWithTimeStamp:(MusicTimeStamp)timeStamp tempo:(Float64)bpm;
 
 /**
  *  The beats per minute of the tempo event.
@@ -37,7 +40,9 @@
 @interface MIKMutableMIDITempoEvent : MIKMIDITempoEvent
 
 @property (nonatomic, readwrite) MusicTimeStamp timeStamp;
-@property (nonatomic, strong, readwrite) NSMutableData *data;
+@property (nonatomic, strong, readwrite, null_resettable) NSMutableData *data;
 @property (nonatomic, readwrite) Float64 bpm;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDITrack.h b/Source/MIKMIDITrack.h
index 49310fca..6be539f2 100644
--- a/Source/MIKMIDITrack.h
+++ b/Source/MIKMIDITrack.h
@@ -8,12 +8,15 @@
 
 #import <Foundation/Foundation.h>
 #import <AudioToolbox/AudioToolbox.h>
+#import "MIKMIDICompilerCompatibility.h"
 
 @class MIKMIDISequence;
 @class MIKMIDIEvent;
 @class MIKMIDINoteEvent;
 @class MIKMIDIDestinationEndpoint;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  Instances of MIKMIDITrack contain sequences of MIDI events. Commonly,
  *  these will be MIDI notes. Multiple MIKMIDITracks can be contained in a
@@ -153,7 +156,7 @@
 /**
  *  The MIDI sequence the track belongs to.
  */
-@property (weak, nonatomic, readonly) MIKMIDISequence *sequence;
+@property (weak, nonatomic, readonly, nullable) MIKMIDISequence *sequence;
 
 /**
  *  The underlying MusicTrack that backs the instance of MIKMIDITrack.
@@ -274,7 +277,7 @@
  *  
  *	The destination endpoint for the MIDI events of the track during playback.
  */
-@property (nonatomic, strong, readwrite) MIKMIDIDestinationEndpoint *destinationEndpoint DEPRECATED_ATTRIBUTE;
+@property (nonatomic, strong, readwrite, nullable) MIKMIDIDestinationEndpoint *destinationEndpoint DEPRECATED_ATTRIBUTE;
 
 /**
  *  @deprecated Use -addEvent: instead.
@@ -319,3 +322,5 @@
 - (BOOL)clearAllEvents DEPRECATED_ATTRIBUTE;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/MIKMIDITrack.m b/Source/MIKMIDITrack.m
index 0c0f9ad6..3c6e40cb 100644
--- a/Source/MIKMIDITrack.m
+++ b/Source/MIKMIDITrack.m
@@ -23,7 +23,7 @@
 
 @interface MIKMIDITrack ()
 
-@property (weak, nonatomic) MIKMIDISequence *sequence;
+@property (weak, nonatomic, nullable) MIKMIDISequence *sequence;
 @property (nonatomic, strong) NSMutableSet *internalEvents;
 @property (nonatomic, strong) NSArray *sortedEventsCache;
 
@@ -321,12 +321,12 @@ - (NSArray *)eventsOfClass:(Class)eventClass fromTimeStamp:(MusicTimeStamp)start
 		events = mutableEvents;
 	}];
 
-	return events;
+	return events ?: @[];
 }
 
 - (NSArray *)eventsFromTimeStamp:(MusicTimeStamp)startTimeStamp toTimeStamp:(MusicTimeStamp)endTimeStamp
 {
-	return [self eventsOfClass:Nil fromTimeStamp:startTimeStamp toTimeStamp:endTimeStamp];
+	return [self eventsOfClass:[MIKMIDIEvent class] fromTimeStamp:startTimeStamp toTimeStamp:endTimeStamp];
 }
 
 - (NSArray *)notesFromTimeStamp:(MusicTimeStamp)startTimeStamp toTimeStamp:(MusicTimeStamp)endTimeStamp
@@ -538,7 +538,7 @@ - (NSArray *)events
 		events = self.sortedEventsCache;
 	}];
 
-	return events;
+	return events ?: @[];
 }
 
 - (void)setEvents:(NSArray *)events
diff --git a/Source/MIKMIDITrack_Protected.h b/Source/MIKMIDITrack_Protected.h
index 68755f98..6bbeff4a 100644
--- a/Source/MIKMIDITrack_Protected.h
+++ b/Source/MIKMIDITrack_Protected.h
@@ -7,6 +7,9 @@
 //
 
 #import "MIKMIDITrack.h"
+#import "MIKMIDICompilerCompatibility.h"
+
+NS_ASSUME_NONNULL_BEGIN
 
 @interface MIKMIDITrack ()
 
@@ -19,7 +22,7 @@
  *  @note You should not call this method. It is for internal MIKMIDI use only.
  *  To add a new track to a MIDI sequence use -[MIKMIDISequence addTrack].
  */
-+ (instancetype)trackWithSequence:(MIKMIDISequence *)sequence musicTrack:(MusicTrack)musicTrack;
++ (nullable instancetype)trackWithSequence:(MIKMIDISequence *)sequence musicTrack:(MusicTrack)musicTrack;
 
 /**
  *  Sets a temporary length and loopInfo for the track.
@@ -39,3 +42,5 @@
 - (void)restoreLengthAndLoopInfo;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/Source/NSUIApplication+MIKMIDI.h b/Source/NSUIApplication+MIKMIDI.h
index 8e3a3d1a..58bf9513 100644
--- a/Source/NSUIApplication+MIKMIDI.h
+++ b/Source/NSUIApplication+MIKMIDI.h
@@ -24,6 +24,8 @@
 
 #endif
 
+#import "MIKMIDICompilerCompatibility.h"
+
 /**
  *  Define MIKMIDI_SEARCH_VIEW_HIERARCHY_FOR_RESPONDERS as a non-zero value to (re)enable searching
  *  the view hierarchy for MIDI responders. This is disabled by default because it's slow.
@@ -36,6 +38,8 @@
 
 @class MIKMIDICommand;
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  *  MIKMIDI implements a category on NSApplication (on OS X) or UIApplication (on iOS)
  *  to facilitate the creation and use of a MIDI responder hierarchy, along with the ability
@@ -108,7 +112,7 @@
  *  @return An object that conforms to MIKMIDIResponder, or nil if no registered responder for the passed in identifier
  *  could be found.
  */
-- (id<MIKMIDIResponder>)MIDIResponderWithIdentifier:(NSString *)identifier;
+- (nullable id<MIKMIDIResponder>)MIDIResponderWithIdentifier:(NSString *)identifier;
 
 /**
  *  Returns all MIDI responders that have been registered with the application.
@@ -135,3 +139,5 @@
 @property (nonatomic) BOOL shouldCacheMIKMIDISubresponders;
 
 @end
+
+NS_ASSUME_NONNULL_END
\ No newline at end of file