'Parses the queue.yaml file.
Args:
basepath: the directory of the application.
appyaml: The app.yaml, if present.
Returns:
A QueueInfoExternal object or None if the file does not exist.'

def _ParseQueueYaml(self, basepath, appyaml=None):

    queue_yaml = self._ParseYamlFile(basepath, 'queue', queueinfo.LoadSingleQueue)
    if (not queue_yaml):
        return None
    self._SetApplication(queue_yaml, 'queue', appyaml)
    return queue_yaml
