Using the test dataset in learn.get_preds() without is_test=True

when I runlearn.get_preds(ds_type=DatasetType.Test, with_loss=True)
I get an IndexError
IndexError Traceback (most recent call last)
in
----> 1 learn.get_preds(ds_type=DatasetType.Test, with_loss=True)

/opt/conda/envs/fastai/lib/python3.6/site-packages/fastai/basic_train.py in get_preds(self, ds_type, activ, with_loss, n_batch, pbar)
    337         callbacks = [cb(self) for cb in self.callback_fns + listify(defaults.extra_callback_fns)] + listify(self.callbacks)
    338         return get_preds(self.model, self.dl(ds_type), cb_handler=CallbackHandler(callbacks),
--> 339                          activ=activ, loss_func=lf, n_batch=n_batch, pbar=pbar)
    340 
    341     def pred_batch(self, ds_type:DatasetType=DatasetType.Valid, batch:Tuple=None, reconstruct:bool=False,

/opt/conda/envs/fastai/lib/python3.6/site-packages/fastai/basic_train.py in get_preds(model, dl, pbar, cb_handler, activ, loss_func, n_batch)
     42     "Tuple of predictions and targets, and optional losses (if `loss_func`) using `dl`, max batches `n_batch`."
     43     res = [to_float(torch.cat(o).cpu()) for o in
---> 44            zip(*validate(model, dl, cb_handler=cb_handler, pbar=pbar, average=False, n_batch=n_batch))]
     45     if loss_func is not None:
     46         with NoneReduceOnCPU(loss_func) as lf: res.append(lf(res[0], res[1]))

/opt/conda/envs/fastai/lib/python3.6/site-packages/fastai/basic_train.py in validate(model, dl, loss_func, cb_handler, pbar, average, n_batch)
     55         val_losses,nums = [],[]
     56         if cb_handler: cb_handler.set_dl(dl)
---> 57         for xb,yb in progress_bar(dl, parent=pbar, leave=(pbar is not None)):
     58             if cb_handler: xb, yb = cb_handler.on_batch_begin(xb, yb, train=False)
     59             val_loss = loss_batch(model, xb, yb, loss_func, cb_handler=cb_handler)

/opt/conda/envs/fastai/lib/python3.6/site-packages/fastprogress/fastprogress.py in __iter__(self)
     70         self.update(0)
     71         try:
---> 72             for i,o in enumerate(self._gen):
     73                 if i >= self.total: break
     74                 yield o

/opt/conda/envs/fastai/lib/python3.6/site-packages/fastai/basic_data.py in __iter__(self)
     73     def __iter__(self):
     74         "Process and returns items from `DataLoader`."
---> 75         for b in self.dl: yield self.proc_batch(b)
     76 
     77     @classmethod

/opt/conda/envs/fastai/lib/python3.6/site-packages/torch/utils/data/dataloader.py in __next__(self)
    817             else:
    818                 del self.task_info[idx]
--> 819                 return self._process_data(data)
    820 
    821     next = __next__  # Python 2 compatibility

/opt/conda/envs/fastai/lib/python3.6/site-packages/torch/utils/data/dataloader.py in _process_data(self, data)
    844         self._try_put_index()
    845         if isinstance(data, ExceptionWrapper):
--> 846             data.reraise()
    847         return data
    848 

/opt/conda/envs/fastai/lib/python3.6/site-packages/torch/_utils.py in reraise(self)
    367             # (https://bugs.python.org/issue2651), so we work around it.
    368             msg = KeyErrorMessage(msg)
--> 369         raise self.exc_type(msg)

IndexError: Caught IndexError in DataLoader worker process 0.
Original Traceback (most recent call last):
  File "/opt/conda/envs/fastai/lib/python3.6/site-packages/torch/utils/data/_utils/worker.py", line 178, in _worker_loop
    data = fetcher.fetch(index)
  File "/opt/conda/envs/fastai/lib/python3.6/site-packages/torch/utils/data/_utils/fetch.py", line 44, in fetch
    data = [self.dataset[idx] for idx in possibly_batched_index]
  File "/opt/conda/envs/fastai/lib/python3.6/site-packages/torch/utils/data/_utils/fetch.py", line 44, in <listcomp>
    data = [self.dataset[idx] for idx in possibly_batched_index]
  File "/opt/conda/envs/fastai/lib/python3.6/site-packages/fastai/data_block.py", line 651, in __getitem__
    if self.item is None: x,y = self.x[idxs],self.y[idxs]
  File "/opt/conda/envs/fastai/lib/python3.6/site-packages/fastai/data_block.py", line 120, in __getitem__
    if isinstance(idxs, Integral): return self.get(idxs)
  File "/opt/conda/envs/fastai/lib/python3.6/site-packages/fastai/vision/data.py", line 270, in get
    fn = super().get(i)
  File "/opt/conda/envs/fastai/lib/python3.6/site-packages/fastai/data_block.py", line 75, in get
    return self.items[i]
IndexError: index 0 is out of bounds for axis 0 with size 0