ValueError when adding opil.SampleSet to opil.ExperimentalRequest

[tramyn]

I'm getting this error when adding opil.SampleSets to opil.ExperimentalRequest.sample_set:
ValueError: SampleSet already has identity https://sd2e.org/ip95ad7d38ca77416a9d7307e277561098 and cannot be re-parented.

[tramyn]

stack trace:

experimental_request.sample_set = self.opil_sample_sets
  File "/lib/python3.7/site-packages/sbol3/object.py", line 23, in __setattr__
    self.__dict__[name].set(value)
  File "/lib/python3.7/site-packages/sbol3/property_base.py", line 181, in set
    self.item_added(val)
  File "/lib/python3.7/site-packages/sbol3/ownedobject.py", line 47, in item_added
    item._update_identity(new_url, new_display_id)
  File "/lib/python3.7/site-packages/sbol3/identified.py", line 105, in _update_identity
    raise ValueError(msg)