hello,I have some mistakes with your code

[peijinwang]

Traceback (most recent call last):
File "./deeplab.py", line 74, in
main()
File "./deeplab.py", line 64, in main
epoch_end_callback = mx.callback.do_checkpoint(deeplab_model_prefix)
File "/.../homework/mxnet-deeplab/solver.py", line 108, in fit
self.updater(key, arr, self.arg_params[key])
File "/.../mxnet/0.7.0/python/mxnet/optimizer.py", line 1472, in call
self.optimizer.update_multi_precision(index, weight, grad, self.states[index])
File "/.../mxnet/0.7.0/python/mxnet/optimizer.py", line 536, in update_multi_precision
multi_precision=use_multi_precision)
File "/.../mxnet/0.7.0/python/mxnet/optimizer.py", line 504, in _update_impl
assert(isinstance(grad, NDArray))
AssertionError

can you help me? thank you!