'Validates the given /isserving YAML string.
Args:
resp: the response from an RPC to a URL such as /api/appversion/isserving.
Returns:
The resulting dictionary if the response is valid, or None otherwise.'

@staticmethod
def _ValidateIsServingYaml(resp):

    response_dict = yaml.safe_load(resp)
    if ('serving' not in response_dict):
        return None
    return response_dict
