code: def is_2dlist(x):
      """check x is 2d-list([[1], []]) or 1d empty list([]).
  
      Notice:
          The reason that it contains 1d empty list is because
          some arguments from gt annotation file or model prediction
          may be empty, but usually, it should be 2d-list.
      """
      if not isinstance(x, list):
          return False
      if len(x) == 0:
          return True
  
      return all(isinstance(item, list) for item in x)
  
label_desc: Use image node_id 2 for calling a global function with example usage: is_2dlist(x) and returns: all, False, True