---
id: SCH-9
family: GR-SCHEMA
level: core
profiles: [storage-api, editor-client]
posture: normative-target
added: "1.0"
changed: "1.0"
source: https://flowdrop.io/spec/rules/gr-schema/sch-9
specification: FlowDrop Workflow Specification 1.0-draft
licence: CC BY 4.0
---

# SCH-9 — A union type resolves to its first non-null member

*GR-SCHEMA (Part I) · level: core · profiles: storage-api, editor-client · added in 1.0*

## The rule

> **Normative.** This is the rule.
>
> 1. Where a property's type is an array of types, its lane is derived from the first member that is not `null`.
>
> 2. An array that is empty, or that holds only `null`, resolves to the sink.
>
> 3. Every member must itself be a JSON Schema type.

## Related rules

- Names: SCH-34, SCH-35
- Referenced by: SCH-34, SCH-35

---

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.