orders|length in t-value parses as orders | length, not as a Jinja length filter. orders is a sale.order recordset; the `length` identifier resolves to None; Python evaluates recordset | None and raises TypeError. Use len(orders) instead. Also documents the gotcha in CLAUDE.md (rule 19) so future templates don't reach for Jinja-style filters in t-value. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>