Merge pull request #47 from mpaulsonco/fix/null-date-crash

#46 fixed MCJSONDateTransformer crash when processing nil dates

Author: matthewcheok

Realm+JSON/MCJSONDateTransformer.m

@@ -64,6 +64,7 @@ + (BOOL)allowsReverseTransformation {
 }
 
 - (id)transformedValue:(id)value {
+    if([value isKindOfClass:[NSNull class]])return nil;
 	return [self.formatter dateFromString:value];
 }