Decode empty message to nil in standard codec

shell/platform/darwin/common/framework/Source/FlutterCodecs.mm

@@ -78,7 +78,7 @@ - (NSData*)encode:(id)message {
 }
 
 - (id)decode:(NSData*)message {
-  if (message == nil)
+  if ([message length] == 0)
     return nil;
   BOOL isSimpleValue = NO;
   id decoded = nil;

shell/platform/darwin/common/framework/Source/FlutterStandardCodec.mm

@@ -45,7 +45,7 @@ - (NSData*)encode:(id)message {
 }
 
 - (id)decode:(NSData*)message {
-  if (message == nil)
+  if ([message length] == 0)
     return nil;
   FlutterStandardReader* reader = [_readerWriter readerWithData:message];
   id value = [reader readValue];

shell/platform/darwin/common/framework/Source/flutter_codecs_unittest.mm

@@ -42,6 +42,11 @@
   ASSERT_TRUE([value isEqualTo:decoded]);
 }
 
+TEST(FlutterJSONCodec, CanDecodeZeroLength) {
+  FlutterJSONMessageCodec* codec = [FlutterJSONMessageCodec sharedInstance];
+  ASSERT_TRUE([codec decode:[NSData data]] == nil);
+}
+
 TEST(FlutterJSONCodec, CanEncodeAndDecodeNil) {
   FlutterJSONMessageCodec* codec = [FlutterJSONMessageCodec sharedInstance];
   ASSERT_TRUE([codec encode:nil] == nil);

shell/platform/darwin/common/framework/Source/flutter_standard_codec_unittest.mm

@@ -30,6 +30,12 @@ void checkEncodeDecode(id value) {
     ASSERT_TRUE([value isEqual:decoded]);
 }
 
+TEST(FlutterStandardCodec, CanDecodeZeroLength) {
+  FlutterStandardMessageCodec* codec = [FlutterStandardMessageCodec sharedInstance];
+  id decoded = [codec decode:[NSData data]];
+  ASSERT_TRUE(decoded == nil);
+}
+
 TEST(FlutterStandardCodec, CanEncodeAndDecodeNil) {
   checkEncodeDecode(nil, nil);
 }

shell/platform/darwin/macos/framework/Source/FlutterEngine.mm

@@ -495,9 +495,12 @@ - (void)sendUserLocales {
 }
 
 - (void)engineCallbackOnPlatformMessage:(const FlutterPlatformMessage*)message {
-  NSData* messageData = [NSData dataWithBytesNoCopy:(void*)message->message
-                                             length:message->message_size
-                                       freeWhenDone:NO];
+  NSData* messageData = nil;
+  if (message->message_size > 0) {
+    messageData = [NSData dataWithBytesNoCopy:(void*)message->message
+                                       length:message->message_size
+                                 freeWhenDone:NO];
+  }
   NSString* channel = @(message->channel);
   __block const FlutterPlatformMessageResponseHandle* responseHandle = message->response_handle;