ClassificationInterpreter AttributeError for custom dataset

I’m using fastai library with custom PyTorch dataset, which I specified the following way (... are there for the purpose of clarity):

from fastai import *

class CustomDataset(Dataset):
    
    def __init__(self, input_path):
        ...
        
    def __len__(self):
        ...

    def __getitem__(self, idx):
        ...
        return (
            torch.tensor(image, dtype=torch.float),
            torch.tensor(target, dtype=torch.long)
        )

train_dset = CustomDataset(train_path)
valid_dset = CustomDataset(valid_path)

train_dl = DataLoader(train_dset, bs=16, shuffle=True)
valid_dl = DataLoader(valid_dset, bs=16, shuffle=True)

dls = DataLoaders(train_dl, valid_dl)

Then I’m using those dataloaders to train the model with Learner:

learn = Learner(dls, model, loss_func=CrossEntropyLossFlat(), metrics=accuracy)
learn.fit_one_cycle(1, 0.01)

and I pass learn object to ClassificationInterpretation class:

interp = ClassificationInterpretation.from_learner(learn)

However, this results in the AttributeError with not so clear details:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-98-aa7f7b70a42b> in <module>
----> 1 interp = ClassificationInterpretation.from_learner(learn)

~/anaconda3/envs/python3/lib/python3.6/site-packages/fastai/interpret.py in from_learner(cls, learn, ds_idx, dl, act)
     40         _,_,losses = learn.get_preds(dl=dl, with_input=False, with_loss=True, with_decoded=False,
     41                                      with_preds=False, with_targs=False, act=act)
---> 42         return cls(learn, dl, losses, act)
     43 
     44     def top_losses(self, k=None, largest=True, items=False):

~/anaconda3/envs/python3/lib/python3.6/site-packages/fastai/interpret.py in __init__(self, learn, dl, losses, act)
     78     def __init__(self, learn, dl, losses, act=None):
     79         super().__init__(learn, dl, losses, act)
---> 80         self.vocab = self.dl.vocab
     81         if is_listy(self.vocab): self.vocab = self.vocab[-1]
     82 

~/anaconda3/envs/python3/lib/python3.6/site-packages/fastcore/basics.py in __getattr__(self, k)
    387         if self._component_attr_filter(k):
    388             attr = getattr(self,self._default,None)
--> 389             if attr is not None: return getattr(attr,k)
    390         raise AttributeError(k)
    391     def __dir__(self): return custom_dir(self,self._dir())

~/anaconda3/envs/python3/lib/python3.6/site-packages/torch/utils/data/dataset.py in __getattr__(self, attribute_name)
     81             return function
     82         else:
---> 83             raise AttributeError
     84 
     85     @classmethod

AttributeError: 

It seems like both data loaders should have additional attribute vocab which might be there for DataBlock output, but not for my custom definition of data loaders. Is that really a problem? How this property should look like and how it could be added to make it compatible with ClassificationInterpreter?