def _from_base_type(self, value):
if not value:<EOL><INDENT>return None<EOL><DEDENT>try:<EOL><INDENT>credentials = client.Credentials.new_from_json(value)<EOL><DEDENT>except ValueError:<EOL><INDENT>credentials = None<EOL><DEDENT>return credentials<EOL>
Converts our stored JSON string back to the desired type.

        Args:
            value: A value from the datastore to be converted to the
                   desired type.

        Returns:
            A deserialized Credentials (or subclass) object, else None if
            the value can't be parsed.