class_docstr: 不进行任何 检查 与 pad 的空 padder 。
  
  :param ele_dtype:
  :param pad_val:
  :param dtype:
code: def __call__(self, batch_field):
      # 直接返回，不调用 pad() 方法加快速度。
      return batch_field
  
label_desc: Use image node_id 2 for calling the NullPadder obj's underlying member method code with example usage: obj.__call__(batch_field) and returns: batch_field