When using gabbihtml a deprecation warning is issued

[cdent]

The warning is:

gabbi/case.py:648: FutureWarning: The behavior of this method will change in future versions. Use specific 'len(elem)' or 'elem is not None' test instead.

It's checking self.response_data and because that's an lxml result at that point it makes that warning. It's likely we can check None as advised there, or len. Depends on if we ever expect an empty string. The existing tests will probably help check the change.