added json check stacks

[kurtbrose]

for comparison, here's what json.dumps() does the the two error stacks added:

>>> json.dumps({'a': [{'b': {1: 2}}]})
'{"a": [{"b": {"1": 2}}]}'
>>> json.dumps({'a': [{'b': 1j}]})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Program Files\Python37\Lib\json\__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
  File "C:\Program Files\Python37\Lib\json\encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "C:\Program Files\Python37\Lib\json\encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "C:\Program Files\Python37\Lib\json\encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type complex is not JSON serializable

[mahmoud]

Interesting stress testing. Lil bit worried about maintenance, but this is as good a guess of what advanced matching specs might look like post rollout.

[mahmoud]

hmm what's goin on with this line?