ZeroDivisionError: float division by zero

[AliSharififar]

hello
Thank you for the models you provided in the field of semantic segmentation. I encounter this error while training hamnet_van_base_512x512_160k_ade20k model using Custom Dataset. I have two more classes. Separated from the background, I made 20K as the ade20k dataset. In debugging, I saw that the addressing of the data set was correct.
Please help me.
correct_k.mul_(100.0 / target[target != ignore_index].numel())) ZeroDivisionError: float division by zero