IndexError: list index out of range

[ari9dam]

For some sentences I am getting this error,
span_outputs = self._model.span_detector.forward_on_instances(instances)
File "/anaconda2/envs/qasrl/lib/python3.6/site-packages/allennlp/models/model.py", line 150, in forward_on_instances
model_input = dataset.as_tensor_dict(cuda_device=cuda_device)
File "/anaconda2/envs/qasrl/lib/python3.6/site-packages/allennlp/data/dataset.py", line 147, in as_tensor_dict
field_classes = self.instances[0].fields
IndexError: list index out of range

Is it because Spacy failed to find any `verb'? (allenai/allennlp#996)

Is there any way pass sentence along with POS?

Thank you