c_tf_idf_ is None when using zero shot topic modeling.

Nobody has claimed this yet.

I am using zero shot topic modeling using bertopic and i also want hierarchical topic representation but When i run the model.hierarchical_topics(array of strings) the following errors is what i get:

TypeError: 'NoneType' object is not subscriptable
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
File , line 1
----> 1 model.hierarchical_topics(array of strings)

File /local_disk0/.ephemeral_nfs/cluster_libraries/python/lib/python3.10/site-packages/bertopic/_bertopic.py:975, in BERTopic.hierarchical_topics(self, docs, linkage_function, distance_function)
972 linkage_function = lambda x: sch.linkage(x, 'ward', optimal_ordering=True)
974 # Calculate distance
--> 975 embeddings = self.c_tf_idf_[self._outliers:]
976 X = distance_function(embeddings)
977 X = validate_distance_matrix(X, embeddings.shape[0])

TypeError: 'NoneType' object is not subscriptable

Start in _bertopic.py at BERTopic.hierarchical_topics, especially the c_tf_idf_ access around line 975, and trace how zero-shot topic modeling initializes that attribute. Reproduce the reported call with the provided document array and verify that hierarchical topic representation no longer fails when c_tf_idf_ is None.

Written by the indexing model from the issue text.