Merge d4a4d9b1880a57d1a6c577e5a27422ce1b334fb2 into 4e714f9df1ed2cccd51df60d45ff5504abe827b7

youtube_dl/jsinterp.py

@@ -686,8 +686,6 @@ class JSInterpreter(object):
             raise self.Exception('Cannot get index {idx!r:.100}'.format(**locals()), expr=repr(obj), cause=e)
 
     def _dump(self, obj, namespace):
-        if obj is JS_Undefined:
-            return 'undefined'
         try:
             return json.dumps(obj)
         except TypeError: