Fix bug in TextGeneration prompt creation when prompt template does not contain [DOCUMENTS]

[manveersadhal]

Prevent attempted iteration over NoneType when prompt template does not contain [DOCUMENTS] in TextGeneration class.

When DEFAULT_PROMPT is used or the user-provided prompt does not contain "[DOCUMENTS]", all of the values in repr_docs_mappings are None. When defining truncated_docs, iteration is attempted over NoneType. This change prevents the attempted iteration and instead passes the None value to _create_prompt.

[manveersadhal]

This is to address issue #1720

[MaartenGr]

Thanks for sharing this fix! Do you by chance have a reproducible example that allows me to test whether this test works for the issue that you are facing?

[manveersadhal]

Hi @MaartenGr . Sure - here is a minimal example I used to test based on the issue submitted (#1720). I tested with the default prompt, the prompt in the issue (although it seems that was not passed to TextGeneration in the example), and another variant including [DOCUMENTS].

from bertopic import BERTopic
from transformers import pipeline
from bertopic.representation import TextGeneration
from sklearn.datasets import fetch_20newsgroups

prompt = "I have a topic described by the following keywords: [KEYWORDS]. What is this topic about?"

# Create your representation model
generator = pipeline('text2text-generation', model='google/flan-t5-small')
representation_model = TextGeneration(generator, prompt=prompt)

topic_model_t5 = BERTopic(representation_model=representation_model)
newsgroup_docs = fetch_20newsgroups(subset='all',  remove=('headers', 'footers', 'quotes'))['data'][:100]

topics, probs = topic_model_t5.fit_transform(newsgroup_docs)
print(topic_model_t5.get_topic_info())

[MaartenGr]

Thanks for the PR, works great!

[leoschet]

Any idea when this will be released?

[MaartenGr]

@leoschet It is merged, so you can install BERTopic from the main branch. An official release might take a while since there are a couple PRs open that need to be merged/checked.

[leoschet]

I've been doping that, just not always possible to pin main for the package version.