ValueError: need at least one array to concatenate

INFO:test2:====> Epoch: 200 [2023-08-26 18:18:25] | (0:00:20.367071)
INFO:test2:Training is done. The program is closed.
INFO:test2:saving final ckpt:Success.
Traceback (most recent call last):
File "C:\Users\Catalin\Desktop\RVC0813AMD_Intel\RVC0813AMD_Intel\runtime\lib\site-packages\gradio\routes.py", line 321, in run_predict
output = await app.blocks.process_api(
File "C:\Users\Catalin\Desktop\RVC0813AMD_Intel\RVC0813AMD_Intel\runtime\lib\site-packages\gradio\blocks.py", line 1006, in process_api
result = await self.call_function(fn_index, inputs, iterator, request)
File "C:\Users\Catalin\Desktop\RVC0813AMD_Intel\RVC0813AMD_Intel\runtime\lib\site-packages\gradio\blocks.py", line 859, in call_function
prediction = await anyio.to_thread.run_sync(
File "C:\Users\Catalin\Desktop\RVC0813AMD_Intel\RVC0813AMD_Intel\runtime\lib\site-packages\anyio\to_thread.py", line 31, in run_sync
return await get_asynclib().run_sync_in_worker_thread(
File "C:\Users\Catalin\Desktop\RVC0813AMD_Intel\RVC0813AMD_Intel\runtime\lib\site-packages\anyio_backends_asyncio.py", line 937, in run_sync_in_worker_thread
return await future
File "C:\Users\Catalin\Desktop\RVC0813AMD_Intel\RVC0813AMD_Intel\runtime\lib\site-packages\anyio_backends_asyncio.py", line 867, in run
result = context.run(func, *args)
File "C:\Users\Catalin\Desktop\RVC0813AMD_Intel\RVC0813AMD_Intel\runtime\lib\site-packages\gradio\utils.py", line 408, in async_iteration
return next(iterator)
File "C:\Users\Catalin\Desktop\RVC0813AMD_Intel\RVC0813AMD_Intel\infer-web.py", line 1283, in train1key
big_npy = np.concatenate(npys, 0)
File "<array_function internals>", line 180, in concatenate
ValueError: need at least one array to concatenate

Start at infer-web.py line 1283, where training calls np.concatenate(npys, 0), and trace how npys is populated before that point. Reproduce the training flow using the issue's log context, determine why no arrays are available, and verify that training completes without the ValueError.