Return the function policy for a lambda function.

        This function will extract the policy string as a json document
        and return the json.loads(...) version of the policy.

def get_function_policy(self, function_name):
        # type: (str) -> Dict[str, Any]
        """Return the function policy for a lambda function.

        This function will extract the policy string as a json document
        and return the json.loads(...) version of the policy.

        """
        client = self._client('lambda')
        try:
            policy = client.get_policy(FunctionName=function_name)
            return json.loads(policy['Policy'])
        except client.exceptions.ResourceNotFoundException:
            return {'Statement': []}