'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.'

def _from_base_type(self, value):

    if (not value):
        return None
    try:
        credentials = client.Credentials.new_from_json(value)
    except ValueError:
        credentials = None
    return credentials
