def num_clusters(self):
        raise NotImplementedError()
Invoke list_trim() with bin is none
dataset/ETHPy150Open nltk/nltk/nltk/cluster/api.py/ClusterI.num_clusters--crossover with--dataset/ETHPy150Open aerospike/aerospike-client-python/test/old_tests/_test_list_trim.py/TestListTrim.test_list_trim_bin_is_none