fix: prevent CitationMixin crash when context missing 'context' key

[truecallerabreham]

Summary

Fix CitationMixin.validate_sources crash when validation_context is provided but doesn't contain the expected "context" key.

Problem

validate_sources calls info.context.get("context", None) which returns None if the key is missing. This None is passed to get_spans(None), which calls _get_span(quote, None), which calls regex.search(pattern, None) — raising TypeError: expected string or bytes-like object.

Fix

Add if text_chunks is None: return self after the .get() call (1 line).

Test

Added tests/dsl/test_citation.py with 3 regression tests covering:

• Missing "context" key in validation_context
• None context
• Normal operation with valid context

Issue

Closes #2459

[ErenAta16]

Correcting my own review on #2492: I described that as one of two PRs for #2459 when there are actually four, and this one predates all of them by eight days. My duplicate check was too shallow, apologies.

The fix here is right, and identical in substance to #2488 and #2492: info.context.get("context", None) returns None when the validation context exists but has no context key, and both downstream uses assume a string:

regex.search('(quote){e<=0}', None) -> TypeError: expected string or buffer

with text_chunks[span[0]:span[1]] failing on None right after. Returning early is the correct shape, and it matches the info.context is None guard already two lines up.

Comparing the four for whoever triages:

PR	date	test	notes
#2460 (this)	Jul 18	yes, new tests/dsl/test_citation.py	earliest
#2471	Jul 20	-	closed
#2488	Jul 26	yes, in existing coverage file	adds CHANGELOG entry
#2492	Jul 27	no

This one has priority by date and ships a test. The only thing #2488 carries that this doesn't is the CHANGELOG line, which is trivial to add here. I'd land this one.

[jxnl]

Closed as a duplicate implementation. The citation-context fix and regression coverage shipped in #2495 via the consolidated canonical patch.