Expected concatenating dimensions in the range [0, 0), but got 0

[cyril10xds]

Hi,
I am facing an issue is while the time of custom training.
code

num_questions = 5
questions = [q for q, a in fastqa_train_data]
for q, a in zip(questions[:num_questions], fastqa_reader(questions)): # Error from this line
print("Question: " + q.question)
print("Answer: %s \t (score: %.3f)\n" % (a[0].text, a[0].score))

error

InvalidArgumentError (see above for traceback): ConcatOp : Expected concatenating dimensions in the range [0, 0), but got 0
[[Node: jtreader/fast_qa/cond_1/segment_top_k/concat = ConcatV2[N=2, T=DT_INT64, Tidx=DT_INT32, _device="/job:localhost/replica:0/task:0/device:CPU:0"](jtreader/fast_qa/cond_1/segment_top_k/Squeeze, jtreader/fast_qa/cond_1/segment_top_k/sub_1, jtreader/fast_qa/cond_1/segment_top_k/concat/axis)]]