'Creates a null session which acts as a replacement object if the
real session support could not be loaded due to a configuration
error.  This mainly aids the user experience because the job of the
null session is to still support lookup without complaining but
modifications are answered with a helpful error message of what
failed.
This creates an instance of :attr:`null_session_class` by default.'

def make_null_session(self, app):

    return self.null_session_class()
