A workflow list-literal expression with a trailing (or leading/double) comma —
'{{ [1, 2,] }}' — evaluated to [1, 2, None]: _split_top_level_commas returns a
trailing empty segment, which _evaluate_simple_expression resolves as an empty
dot-path to None. That silently widens membership tests and renders a stray
None in joins. Python and Jinja2 both tolerate trailing commas.
Drop whitespace-empty segments from the comprehension. An intentional
empty-string element ('') survives because its segment strips to "''" (truthy),
so ['', 'a'] is preserved. Completes the quoted-comma handling from #3134.
Test: [1, 2,] and [1,, 2] -> [1, 2]; ['', 'a'] -> ['', 'a'] (fails before:
trailing None).
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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