Fixing a field path is only half a mapping repair.

In a small n8n mapping demo, the input email lived inside the nested body object, but the Code node read a top-level email and called .trim(). The batch stopped before producing either result.

The repair started with a contract: • Read the agreed field path. • Validate the container and value types. • Return an accepted or rejected result for every input. • Preserve input linkage, then branch on status before any downstream action.

The repaired two-record sample accepted the valid email and explicitly rejected the null email.

The exact exported code passed 10 Node test groups. A separate n8n 1.121.3 CLI check covered the two-record sample. Those are different checks, and the case study keeps them separate.

AI-assisted, self-built synthetic work, not a client or production result. Full failure, repair and limits: https://contra.com/p/3scsUBAZ-n8n-payload-mapping-repair-explicit-results-for-every-input?r=shivansh_jain_jkup5ikk

Before patching a real workflow, agree what malformed data should do: reject, skip, or stop. Never share credentials or customer records in a public bug report.