code: def _nullcontext():
      """Pre-Python-3.7-compatible standin for contextlib.nullcontext."""
      yield
  
file_path: tensorboard/tensorboard/plugins/graph/graphs_demo.py
imports: import contextlib
  import os
  import tensorflow
  import numpy
label_desc: Use image node_id 1 for calling a global function with example usage: _nullcontext() without return types