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

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

    index_yaml = self._ParseYamlFile(basepath, 'index', datastore_index.ParseIndexDefinitions)
    if (not index_yaml):
        return None
    self._SetApplication(index_yaml, 'index', appyaml)
    return index_yaml
