Reset cached properties. If ``key`` is passed, only clears that key.

def _reset_cache(self, key=None):
        """
        Reset cached properties. If ``key`` is passed, only clears that key.
        """
        if getattr(self, '_cache', None) is None:
            return
        if key is None:
            self._cache.clear()
        else:
            self._cache.pop(key, None)