code: def visualization_type() -> str:
      return "empty"
  
imports: import base64
  import warnings
  from collections import namedtuple
  from io import BytesIO
  from typing import Callable, List, Optional, Union
  from captum._utils.common import safe_div
  from captum.attr._utils import visualization
  from captum.insights.attr_vis._utils.transforms import format_transforms
label_desc: Use image node_id 2 for calling the EmptyFeature obj's underlying member method code with example usage: obj.visualization_type() and returns: str