code: def checkpoint_file():
      """Get the path to the VGG16 checkpoint file from flags.
  
      Returns:
        Path to the VGG checkpoint.
      Raises:
        ValueError: checkpoint is null.
      """
      if FLAGS.vgg_checkpoint is None:
          raise ValueError("VGG checkpoint is None.")
  
      return os.path.expanduser(FLAGS.vgg_checkpoint)
  
imports: import os
  import tensorflow.compat.v1
  import tf_slim
label_desc: Use image node_id 1 for calling a global function with example usage: checkpoint_file() and returns: os