AttributeError: 'NoneType' object has no attribute 'to_play'

[greatken999]

when run "python3 main.py preprocess data/other/tmp/" i get this error info:
3 sgfs found.
Estimated number of chunks: 0
Traceback (most recent call last):
File "main.py", line 94, in
argh.dispatch(parser)
File "/usr/local/lib/python3.5/dist-packages/argh/dispatching.py", line 174, in dispatch
for line in lines:
File "/usr/local/lib/python3.5/dist-packages/argh/dispatching.py", line 277, in _execute_command
for line in result:
File "/usr/local/lib/python3.5/dist-packages/argh/dispatching.py", line 260, in _call
result = function(*positional, **keywords)
File "main.py", line 49, in preprocess
test_chunk, training_chunks = parse_data_sets(*data_sets)
File "/mnt/ken-volume/MuGo/load_data_sets.py", line 140, in parse_data_sets
test_chunk, training_chunks = split_test_training(positions_w_context, est_num_positions)
File "/mnt/ken-volume/MuGo/load_data_sets.py", line 60, in split_test_training
positions_w_context = list(positions_w_context)
File "/mnt/ken-volume/MuGo/load_data_sets.py", line 52, in get_positions_from_sgf
for position_w_context in replay_sgf(f.read()):
File "/mnt/ken-volume/MuGo/sgf_wrapper.py", line 133, in replay_sgf
maybe_correct_next(pos, current_node.next)
File "/mnt/ken-volume/MuGo/sgf_wrapper.py", line 97, in maybe_correct_next
('W' in next_node.properties and not pos.to_play == go.WHITE)):
AttributeError: 'NoneType' object has no attribute 'to_play'