.evaluate() fails with current pandas

[thvitt]

    distances.evaluate()
  File "/tmp/pydelta/delta/deltas.py", line 787, in evaluate
    result["Simple Score"] = self.simple_score()
  File "/tmp/pydelta/delta/deltas.py", line 772, in simple_score
    in_group_df, out_group_df = self.z_scores().partition()
  File "/tmp/pydelta/delta/deltas.py", line 731, in z_scores
    return DistanceMatrix((self - deltas.mean()) / deltas.std(),
  File "/tmp/pydelta/.venv/lib/python3.8/site-packages/pandas/core/ops/__init__.py", line 660, in f
    new_data = dispatch_to_series(self, other, op)
  File "/tmp/pydelta/.venv/lib/python3.8/site-packages/pandas/core/ops/__init__.py", line 266, in dispatch_to_series
    return type(left)(bm)
  File "/tmp/pydelta/delta/deltas.py", line 630, in __init__
    self.metadata = Metadata(metadata, **kwargs)
  File "/tmp/pydelta/delta/util.py", line 31, in __init__
    self.update(*args, **kwargs)
  File "/tmp/pydelta/delta/util.py", line 84, in update
    self._update_from(arg)
  File "/tmp/pydelta/delta/util.py", line 53, in _update_from
    self.__dict__.update(d)
TypeError: 'NoneType' object is not iterable

works for pandas < 0.25

[christofs]

I can confirm that this workaround, i.e. downgrading pandas e.g. to 0.25.3, solves the issue.