---
id: LANG-3
family: GR-LANG
level: core
profiles: [storage-api, runtime]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/gr-lang/lang-3
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# LANG-3 — An empty expression is not an error

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

## The rule

> **Normative.** This is the rule.
>
> 1. An empty expression is valid: it passes validation, and it produces a defined result rather than a failure.
>
> 2. A mapper output whose expression is empty is null, whatever the engine.
>
> 3. An extractor whose path is empty returns its input unchanged, reports success, and reports no match.

---

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.