def _load_from_cache_if_available(self, key):
if key in self._cache:<EOL><INDENT>entity = self._cache[key]  <EOL>if entity is None or entity._key == key:<EOL><INDENT>raise tasklets.Return(entity)<EOL><DEDENT><DEDENT>
Returns a cached Model instance given the entity key if available.

        Args:
          key: Key instance.

        Returns:
          A Model instance if the key exists in the cache.