index out of range in self!

I want to use the pre-trained long-former model to get embeddings for long documents (maximum 5000 words). I am trying to execute the demo on relatively long documents to test the library. The code works if the input text is small. But it gives the following error when executing it for long documents. any help?

**P.S I am running it on a regular CPU**
```
config = LongformerConfig.from_pretrained('longformer-encdec-base-16384/')
config.attention_mode = 'sliding_chunks'
model = LongformerModel.from_pretrained("longformer-encdec-base-16384/")
tokenizer = RobertaTokenizer.from_pretrained('roberta-base')
tokenizer.model_max_length = model.config.max_position_embeddings
SAMPLE_TEXT = ' '.join(['Hello to this world'] * 2000) # long input document

input_ids = torch.tensor(tokenizer.encode(SAMPLE_TEXT)).unsqueeze(0)

attention_mask = torch.ones(input_ids.shape, dtype=torch.long,
device=input_ids.device) # initialize to local attention

input_ids, attention_mask = pad_to_window_size(
input_ids, attention_mask, config.attention_window[0], tokenizer.pad_token_id)
x = model(input_ids, attention_mask=attention_mask)[0]
print(x)
```

> x = modelLong(input_ids, attention_mask=attention_mask)
> File "/Users/omarsayed/PycharmProjects/testLongFormer/venv/lib/python3.8/site-packages/torch/nn/modules/module.py", line 722, in _call_impl
> result = self.forward(*input, **kwargs)
> File "/Users/omarsayed/PycharmProjects/testLongFormer/venv/lib/python3.8/site-packages/transformers/modeling_longformer.py", line 1070, in forward
> embedding_output = self.embeddings(
> File "/Users/omarsayed/PycharmProjects/testLongFormer/venv/lib/python3.8/site-packages/torch/nn/modules/module.py", line 722, in _call_impl
> result = self.forward(*input, **kwargs)
> File "/Users/omarsayed/PycharmProjects/testLongFormer/venv/lib/python3.8/site-packages/transformers/modeling_roberta.py", line 81, in forward
> return super().forward(
> File "/Users/omarsayed/PycharmProjects/testLongFormer/venv/lib/python3.8/site-packages/transformers/modeling_bert.py", line 208, in forward
> position_embeddings = self.position_embeddings(position_ids)
> File "/Users/omarsayed/PycharmProjects/testLongFormer/venv/lib/python3.8/site-packages/torch/nn/modules/module.py", line 722, in _call_impl
> result = self.forward(*input, **kwargs)
> File "/Users/omarsayed/PycharmProjects/testLongFormer/venv/lib/python3.8/site-packages/torch/nn/modules/sparse.py", line 124, in forward
> return F.embedding(
> File "/Users/omarsayed/PycharmProjects/testLongFormer/venv/lib/python3.8/site-packages/torch/nn/functional.py", line 1814, in embedding
> return torch.embedding(weight, input, padding_idx, scale_grad_by_freq, sparse)
> IndexError: index out of range in self