@classmethod
def from_custom_provider(cls, provider, app=None, **kwargs):
    """Create a FlaskMultiRedis instance using a custom Redis provider."""
    assert provider is not None, 'your custom provider is None, come on'
    instance = cls(**kwargs)
    instance.provider_class = provider
    if app is not None:
        instance.init_app(app)
    return instance
