find_topics(topic) crashes if topic is a 1-element list

[raffaelemancuso]

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Desribe the bug

topic_model.find_topics(topic) crashes if topic is a list with 1 string only.

It works if topic is a string or a list of strings with len>1

Reproduction

from bertopic import BERTopic
from sklearn.datasets import fetch_20newsgroups
 
docs = fetch_20newsgroups(subset='all',  remove=('headers', 'footers', 'quotes'))['data']

topic_model = BERTopic()
topics, probs = topic_model.fit_transform(docs)
similar_topics, similarities = topic_model.find_topics(["internet"], top_n=50)

BERTopic Version

0.17.4