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ValueError: need at least one array to concatenate

/root/miniconda3/envs/rvc/lib/python3.10/site-packages/torch/optim/lr_scheduler.py:138: UserWarning: Detected call of `lr_scheduler.step()` before `optimizer.step()`. In PyTorch 1.1.0 and later, you should call them in the opposite order: `optimizer.step()` before `lr_scheduler.step()`.  Failure to do this will result in PyTorch skipping the first value of the learning rate schedule. See more details at https://pytorch.org/docs/stable/optim.html#how-to-adjust-learning-rate
  warnings.warn("Detected call of `lr_scheduler.step()` before `optimizer.step()`. "
Traceback (most recent call last):
  File "/root/miniconda3/envs/rvc/lib/python3.10/site-packages/gradio/routes.py", line 393, in run_predict
    output = await app.get_blocks().process_api(
  File "/root/miniconda3/envs/rvc/lib/python3.10/site-packages/gradio/blocks.py", line 1108, in process_api
    result = await self.call_function(
  File "/root/miniconda3/envs/rvc/lib/python3.10/site-packages/gradio/blocks.py", line 929, in call_function
    prediction = await anyio.to_thread.run_sync(
  File "/root/miniconda3/envs/rvc/lib/python3.10/site-packages/anyio/to_thread.py", line 31, in run_sync
    return await get_asynclib().run_sync_in_worker_thread(
  File "/root/miniconda3/envs/rvc/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 937, in run_sync_in_worker_thread
    return await future
  File "/root/miniconda3/envs/rvc/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 867, in run
    result = context.run(func, *args)
  File "/root/miniconda3/envs/rvc/lib/python3.10/site-packages/gradio/utils.py", line 490, in async_iteration
    return next(iterator)
  File "/root/autodl-tmp/Retrieval-based-Voice-Conversion-WebUI/infer-web.py", line 898, in train1key
    big_npy = np.concatenate(npys, 0)
  File "<__array_function__ internals>", line 180, in concatenate
ValueError: need at least one array to concatenate