fix(workflows): list-literal expression ignores trailing/empty commas (#3631)

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>

src/specify_cli/workflows/expressions.py

@@ -535,6 +535,10 @@ def _evaluate_simple_expression(expr: str, namespace: dict[str, Any]) -> Any:
         items = [
             _evaluate_simple_expression(i.strip(), namespace)
             for i in _split_top_level_commas(inner)
+            # Drop empty segments from trailing/leading/double commas ([1, 2,] ->
+            # [1, 2], not [1, 2, None]). An intentional empty-string element
+            # ('') strips to "''" (truthy), so ['', 'a'] is preserved.
+            if i.strip()
         ]
         return items
 

tests/test_workflows.py

@@ -404,6 +404,17 @@ class TestExpressions:
         assert evaluate_expression('{{ [["a", "b"], "c"] }}', ctx) == [["a", "b"], "c"]
         assert evaluate_expression("{{ [[1, 2], [3, 4]] }}", ctx) == [[1, 2], [3, 4]]
 
+    def test_list_literal_ignores_trailing_and_empty_commas(self):
+        from specify_cli.workflows.expressions import evaluate_expression
+        from specify_cli.workflows.base import StepContext
+
+        ctx = StepContext()
+        # A trailing comma must not append a spurious None element.
+        assert evaluate_expression("{{ [1, 2,] }}", ctx) == [1, 2]
+        assert evaluate_expression("{{ [1,, 2] }}", ctx) == [1, 2]
+        # …but an intentional empty-string element is still preserved.
+        assert evaluate_expression("{{ ['', 'a'] }}", ctx) == ["", "a"]
+
     def test_operator_splitting_is_quote_aware(self):
         from specify_cli.workflows.expressions import (
             evaluate_condition,