code: def test_invalid_writer(self):
      with self.assertRaisesRegex(
          TypeError,
          "writer must be a `SummaryWriter` or `str`, not None",
      ):
          _keras.Callback(writer=None, hparams={})
  
file_path: tensorboard/tensorboard/plugins/hparams/_keras_test.py
imports: import os
  from unittest import mock
  from google.protobuf import text_format
  import tensorflow
  from tensorboard.plugins.hparams import _keras
  from tensorboard.plugins.hparams import metadata
  from tensorboard.plugins.hparams import plugin_data_pb2
  from tensorboard.plugins.hparams import summary_v2
label_desc: Use image node_id 7 for calling the CallbackTest obj's underlying member method code with example usage: obj.test_invalid_writer() without return types