code: def to_python(self, value):
          
          if value is None:
              return None
          elif isinstance(value, oauth2client.client.Credentials):
              return value
          else:
              try:
                  return jsonpickle.decode(
                      base64.b64decode(encoding.smart_bytes(value)).decode())
              except ValueError:
                  return pickle.loads(
                      base64.b64decode(encoding.smart_bytes(value)))
docs: Overrides ``models.Field`` method. This is used to convert
          bytes (from serialization etc) to an instance of this class