Fetch argument None has invalid type <class 'NoneType'>

[prashantgpt91]

Traceback (most recent call last):
  File "bin\iterate\table_adjacency_parsing.py", line 36, in <module>
    trainer.train()
  File "PycharmProjects\TIES-2.0\python\iterators\table_adjacency_parsing_iterator.py", line 85, in train
    model.run_training_iteration(sess, summary_writer, iteration_number)
  File "PycharmProjects\TIES-2.0\python\models\basic_model.py", line 388, in run_training_iteration
    ops_result = sess.run(ops_to_run, feed_dict = feed_dict)
  File "AppData\Local\Continuum\anaconda3\envs\Yvision\lib\site-packages\tensorflow\python\client\session.py", line 929, in run
    run_metadata_ptr)
  File "AppData\Local\Continuum\anaconda3\envs\Yvision\lib\site-packages\tensorflow\python\client\session.py", line 1137, in _run
    self._graph, fetches, feed_dict_tensor, feed_handles=feed_handles)
  File "AppData\Local\Continuum\anaconda3\envs\Yvision\lib\site-packages\tensorflow\python\client\session.py", line 471, in __init__
    self._fetch_mapper = _FetchMapper.for_fetch(fetches)
  File "AppData\Local\Continuum\anaconda3\envs\Yvision\lib\site-packages\tensorflow\python\client\session.py", line 261, in for_fetch
    return _ListFetchMapper(fetch)
  File "AppData\Local\Continuum\anaconda3\envs\Yvision\lib\site-packages\tensorflow\python\client\session.py", line 370, in __init__
    self._mappers = [_FetchMapper.for_fetch(fetch) for fetch in fetches]
  File "AppData\Local\Continuum\anaconda3\envs\Yvision\lib\site-packages\tensorflow\python\client\session.py", line 370, in <listcomp>
    self._mappers = [_FetchMapper.for_fetch(fetch) for fetch in fetches]
  File "AppData\Local\Continuum\anaconda3\envs\Yvision\lib\site-packages\tensorflow\python\client\session.py", line 258, in for_fetch
    type(fetch)))
TypeError: Fetch argument None has invalid type <class 'NoneType'>

Can someone guide, what could possibly be wrong here ?
Train/test/val tfrecords path is correct in config