pydicom.MultiValue not handled properly

When receiving c-find responses containing MultiValue objects, inside my python3 dev environment qrscu crashes immediately with below error message:

Traceback (most recent call last):
  File "qrscu.py", line 1512, in <module>
    qrscu_script()
  File "qrscu.py", line 1489, in qrscu_script
    get_empty_sr=processed_args['get_empty_sr']
  File "qrscu.py", line 912, in qrscu
    modalities_returned, modality_matching = _query_for_each_modality(all_mods, query, d, assoc)
  File "qrscu.py", line 736, in _query_for_each_modality
    _query_study(assoc, d, query, query_id)
  File "qrscu.py", line 666, in _query_study
    rsp.set_modalities_in_study(identifier.ModalitiesInStudy)
  File "/home/openrem/openremrepo/openrem/remapp/models.py", line 283, in set_modalities_in_study
    self.modalities_in_study = json.dumps(x)
  File "/usr/lib/python3.7/json/__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
  File "/usr/lib/python3.7/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/lib/python3.7/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/usr/lib/python3.7/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type MultiValue is not JSON serializable

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Easily reproduced with following code:

from pydicom.multival import MultiValue
import json

multi = MultiValue(str, ["DX", "SR"])

print(json.dumps(multi))

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Replacing pydicom.multival with dicom.multival (pydicom 0.9.9) this code works, but with newer (python3) pydicom versions it fails… not sure if it’s because of python 2 vs 3 or modifications inside the pydicom library.

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