The kernel appears to have died. It will restart automatically when running doc = nlp('')

When running this line of code: doc=nlp('Hello world.') I get this error message: The kernel appears to have died. It will restart automatically

This error occurs only when the text includes spaces.

Here is my code:

import spacy
import neuralcoref

nlp = spacy.load('en')
neuralcoref.add_to_pipe(nlp)

doc = nlp(u'Hello world')

doc._.has_coref
doc._.coref_clusters