Can't load from pickle

[adaldo]

I have an AttributeError when I try to load a FrozenMultiset with pickle.load.
Namely, this code raises an AttributeError on line 118 of multiset.py when trying to access the _elements attribute.

import pickle as pk
import multiset as ms

fms = ms.FrozenMultiset("aabcd")
    
with open("my_file","w") as my_file:
    pk.dump(fms, my_file)

with open("my_file", "r") as my_file:
    fms_copy = pk.load(my_file)

[wheerd]

Version 2.0.3 fixes this problem.