AssertionError: must provide optimizer during init in order to use backward

[tuannvhust]

Traceback (most recent call last):
  File "/opt/bitnami/python/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/opt/bitnami/python/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/workspace/vall-e/vall_e/train.py", line 128, in <module>
    main()
  File "/workspace/vall-e/vall_e/train.py", line 119, in main
    trainer.train(
  File "/workspace/vall-e/vall_e/utils/trainer.py", line 155, in train
    stats = engines.step(feeder=train_feeder, batch=batch)
  File "/workspace/vall-e/vall_e/utils/engines.py", line 156, in step
    engine.backward(loss)
  File "/opt/bitnami/python/lib/python3.10/site-packages/deepspeed/utils/nvtx.py", line 11, in wrapped_fn
    return func(*args, **kwargs)
  File "/opt/bitnami/python/lib/python3.10/site-packages/deepspeed/runtime/engine.py", line 1701, in backward
    assert self.optimizer is not None and not isinstance(self.optimizer, DummyOptim), \
AssertionError: must provide optimizer during init in order to use backward

I got this bug? How should I fix it?