RuntimeError: generator raised StopIteration in Dutch verb conjugation

When running the following code:

import pattern.nl
from pattern.nl import conjugate
from pattern.nl import PRESENT, SG, PAST
conjugate("ben", PRESENT, 3, SG)

I get the following error:

Traceback (most recent call last):
  File "/home/emma/miniconda3/lib/python3.7/site-packages/Pattern-3.6-py3.7.egg/pattern/text/__init__.py", line 609, in _read
    raise StopIteration
StopIteration

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/emma/miniconda3/lib/python3.7/site-packages/Pattern-3.6-py3.7.egg/pattern/text/__init__.py", line 2208, in conjugate
    b = self.lemma(verb, parse=kwargs.get("parse", True))
  File "/home/emma/miniconda3/lib/python3.7/site-packages/Pattern-3.6-py3.7.egg/pattern/text/__init__.py", line 2172, in lemma
    self.load()
  File "/home/emma/miniconda3/lib/python3.7/site-packages/Pattern-3.6-py3.7.egg/pattern/text/nl/inflect.py", line 246, in load
    _Verbs.load(self)
  File "/home/emma/miniconda3/lib/python3.7/site-packages/Pattern-3.6-py3.7.egg/pattern/text/__init__.py", line 2127, in load
    for v in _read(self._path):
RuntimeError: generator raised StopIteration

However, if I run conjugate("ben", PRESENT, 3, SG) again in the same shell it works as expected.

Reproduce the first-call failure with the Dutch conjugation example, then inspect _read and the loading path in pattern/text/init.py and pattern/text/nl/inflect.py. Done means the initial conjugate("ben", PRESENT, 3, SG) call succeeds under the affected Python version, while the existing behavior remains covered by a regression test.