mean_loss: nan need help

[tt960922]

The following two errors occurred when running the old ST-GCN
And mean_loss: nan How to deal with it?
At present, there are 4 types of actions, and there are still mistakes, need help

\fromnumeric.py:3441: RuntimeWarning: Mean of empty slice.
out=out, **kwargs)

_methods.py:189: RuntimeWarning: invalid value encountered in double_scalars