Get the right converter function for Keras

def _get_layer_converter_fn(layer, add_custom_layers = False):
    """Get the right converter function for Keras
    """
    layer_type = type(layer)
    if layer_type in _KERAS_LAYER_REGISTRY:
        convert_func = _KERAS_LAYER_REGISTRY[layer_type]
        if convert_func is _layers2.convert_activation:
            act_name = _layers2._get_activation_name_from_keras_layer(layer)
            if act_name == 'CUSTOM':
                return None
        return convert_func
    elif add_custom_layers:
        return None
    else:
        raise TypeError("Keras layer of type %s is not supported." % type(layer))