AttributeError when executing tests

I encountered an issue when adding the following item specification:

class TestSeriesEpisode(ItemSpec):
    item_cls = EpisodeItem
    test_tv_show_name = Type(str), Match('name')
    test_season_number = Type(int), Required()
    test_episode_number = Type(int), Required()
    test_release_downloadlink_tuples = Required()

For some reason, scrapy-test throws the following error:
AttributeError: 'NoneType' object has no attribute 'values'

Any thoughts on this issue or what I might be doing wrong?

Traceback:

Traceback (most recent call last):
  File "/Users/dennis/Developer/series-scraper/venv/bin/scrapy-test", line 10, in <module>
    sys.exit(main())
  File "/Users/dennis/Developer/series-scraper/venv/lib/python3.7/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/Users/dennis/Developer/series-scraper/venv/lib/python3.7/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/Users/dennis/Developer/series-scraper/venv/lib/python3.7/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/dennis/Developer/series-scraper/venv/lib/python3.7/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/Users/dennis/Developer/series-scraper/venv/lib/python3.7/site-packages/scrapytest/cli.py", line 114, in main
    buffer, failed = validate_spider(spider, results[spider.name], stats[spider.name])
  File "/Users/dennis/Developer/series-scraper/venv/lib/python3.7/site-packages/scrapytest/cli.py", line 148, in validate_spider
    for msg in validator.validate_coverage(results):
  File "/Users/dennis/Developer/series-scraper/venv/lib/python3.7/site-packages/scrapytest/validate.py", line 110, in validate_coverage
    for item_cls, counter in self.count_fields(items).items():
  File "/Users/dennis/Developer/series-scraper/venv/lib/python3.7/site-packages/scrapytest/validate.py", line 98, in count_fields
    for item_cls, count in _count_item(item).items():
  File "/Users/dennis/Developer/series-scraper/venv/lib/python3.7/site-packages/scrapytest/validate.py", line 79, in _count_item
    for value in item.values():
AttributeError: 'NoneType' object has no attribute 'values'