---
id: LANG-29
family: GR-LANG
level: core
profiles: [runtime]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/gr-lang/lang-29
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# LANG-29 — An expression error fails the node; an empty result does not

*GR-LANG (Part I) · level: core · profiles: runtime · added in 1.0*

One policy across every node that evaluates an author's expression, so a broken expression is visible and routable rather than silently absorbed.

## The rule

> **Normative.** This is the rule.
>
> 1. An expression error (a path the engine cannot evaluate, a failure raised by the engine) fails the node, and the failure routes to the error edge.
>
> 2. This holds uniformly across every node that evaluates an author's expression.
>
> 3. An expression that evaluates cleanly and finds nothing is not an error, so an extractor's default-on-no-match is unaffected.
>
> 4. Leniency toward genuine errors is only ever an explicit, opt-in node configuration, never the default.

## Why

Recorded under OPEN-8.

## Related rules

- Names: LANG-21, LANG-22, LANG-24, LANG-25, LANG-26
- Referenced by: LANG-21, LANG-22, LANG-25, LANG-26

---

Rule identifiers are permanent and are never renumbered. This specification carries
no implementation status: each implementation publishes its own standing against
these rules. Licensed CC BY 4.0.