Consider NSNull object as type=null in ObjectMapper.

Summary: nil objects from sqlite is NSNull object, so we need to consider this case in the ObjectMapper as well.

Differential Revision: D48394360

fbshipit-source-id: 61bcdb03cb4cbf17a2fef000a5a61ac2f2c035dd

iOS/Plugins/FlipperKitDatabasesPlugin/FlipperKitDatabasesPlugin/ObjectMapper.m

@@ -127,7 +127,7 @@ static NSString* const UNKNOWN_BLOB_LABEL_FORMAT = @"{%d-byte %@ blob}";
 }
 
 + (NSDictionary*)objectAndTypeToFlipperObject:(id)object {
-  if (!object) {
+  if (!object || [object isKindOfClass:[NSNull class]]) {
     return @{@"type" : @"null"};
   } else if ([object isKindOfClass:[NSNumber class]]) {
     NSNumber* number = (NSNumber*)object;