Your data isn't split, if you don't want a validation set, please use `split_none`

When I tried to run a sample notebook from MultiFit for German, I got the following error:

Exception                                 Traceback (most recent call last)
~/multifit/notebooks/CLS-DE.ipynb in <module>
----> 1 cls_dataset.load_clas_databunch(bs=exp.finetune_lm.bs).show_batch()

~/multifit/multifit/datasets/dataset.py in load_clas_databunch(self, bs, limit)
    224 
    225     def load_clas_databunch(self, bs, limit=None):
--> 226         vocab = self._load_vocab()
    227 
    228         cls_name = "cls"

~/multifit/multifit/datasets/dataset.py in _load_vocab(self)
    220     def _load_vocab(self):
    221         if self._vocab is None:
--> 222             self._vocab = self.load_lm_databunch(bs=20, bptt=70).vocab
    223         return self._vocab
    224 

~/multifit/multifit/datasets/dataset.py in load_lm_databunch(self, bs, bptt, limit)
    207                                               bptt=bptt,
    208                                               bs=bs,
--> 209                                               limit=limit)
    210 
    211         with (self.cache_path / "itos.pkl").open('wb') as f:

~/multifit/multifit/datasets/dataset.py in load_n_cache_databunch(self, name, bunch_class, data_loader, bs, limit, **args)
    260                 train_df = train_df[:limit]
    261                 valid_df = valid_df[:limit]
--> 262             databunch = self.databunch_from_df(bunch_class, train_df, valid_df, **args)
    263             print("name:", name)
    264             databunch.save(name)

~/multifit/multifit/datasets/dataset.py in databunch_from_df(self, bunch_class, train_df, valid_df, **args)
    275                                             mark_fields=True,
    276                                             text_cols=list(train_df.columns.values)[1:],
--> 277                                             **args)
    278         return databunch
    279 

~/multifit/fastai_contrib/text_data.py in make_data_bunch_from_df(cls, path, train_df, valid_df, tokenizer, vocab, classes, text_cols, label_cols, label_delim, chunksize, max_vocab, min_freq, mark_fields, include_bos, include_eos, processor, **kwargs)
    169         else:
    170             src = src.label_from_df(cols=label_cols, classes=classes)
--> 171     return src.databunch(**kwargs)

~/miniconda3/lib/python3.7/site-packages/fastai/data_block.py in databunch(self, **kwargs)
    744     def databunch(self, **kwargs):
    745         "To throw a clear error message when the data wasn't split."
--> 746         raise Exception("Your data isn't split, if you don't want a validation set, please use `split_none`")
    747 
    748 @classmethod

Exception: Your data isn't split, if you don't want a validation set, please use `split_none`