Hi,

I trained a cnn_learner with a custom loss function. Now that I call get_preds on it with test dataset, it returns attribute error.

Here is the error.

Also I did not write the loss function myself, searched and found it. But it was working so I copied it in.

Here is the code:

```
class FocalLoss(nn.Module):
def __init__(self, gamma=2):
super().__init__()
self.gamma = gamma
def forward(self, logit, target):
target = target.float()
max_val = (-logit).clamp(min=0)
loss = logit - logit * target + max_val + \
((-max_val).exp() + (-logit - max_val).exp()).log()
invprobs = F.logsigmoid(-logit * (target * 2.0 - 1.0))
loss = (invprobs * self.gamma).exp() * loss
if len(loss.size())==2:
loss = loss.sum(dim=1)
return loss.mean()
```

I called `learner.loss_fn = FocalLoss()`

to set the loss function.

Could you point out what is causing this error and how I can get around it?