# Act on an empty input

Control / flow

A variant of [Branch or loop](https://meridian.online/operations/branch-or-loop).

Do something different when the input has no rows: emit a placeholder row, switch branch or take another table.

Page: <https://meridian.online/operations/branch-or-loop/act-on-an-empty-input>

## Status

Not built yet.

arcform does not do this yet; it would live in how a Protocol runs. [Its place on the roadmap](https://meridian.online/roadmap#branch-or-loop)

## What other tools call it

Meridian's classification; an independent blind rating agreed on 95.7% of 324 rows (variant, version 3).

- EasyMorph: [`Either table`](https://help.easymorph.com/doku.php?id=transformations:either) (read 2026-09-27)
- Apache Hop: [`Detect Empty Stream`](https://hop.apache.org/manual/latest/pipeline/transforms/detectemptystream.html) (read 2026-09-27)
- KNIME Analytics Platform: [`Empty Table Switch`](https://api.hub.knime.com/nodes/*OuUlAho1iWN4TCEk?details=full) (read 2026-09-27)
- Pentaho Data Integration: [`Detect empty stream`](https://docs.pentaho.com/pdia-data-integration/9.3-data-integration/pdi-transformation-steps-reference-overview) (read 2026-09-27)