39004ERRORTier 2 — Caution✅ HIGH confidence

null value not allowed

Category: External Routine Invocation ExceptionVersions: All Postgres versions

What this means

SQLSTATE 39004 is raised when an external routine declared STRICT returns NULL in a context where NULL is not allowed, or passes NULL to a STRICT function argument.

Why it happens

1An external function declared STRICT is called with a NULL argument (STRICT functions return NULL for any NULL argument without executing — 39004 is raised if this contract is violated)

How to reproduce

STRICT external function receiving a NULL argument explicitly.

trigger — this will ERROR

ERROR: null value not allowed

Fix 1: Filter NULLs before calling STRICT functions

When calling STRICT external functions with nullable data.

fix

SELECT my_strict_fn(col) FROM data WHERE col IS NOT NULL;

Why this works

STRICT functions short-circuit on NULL inputs by convention, but filtering NULLs in SQL prevents the issue entirely.

Sources

📚 Official docs: https://www.postgresql.org/docs/current/errcodes-appendix.html

🔧 Source ref: Class 39 — External Routine Invocation Exception

Confidence assessment

✅ HIGH confidence

Standard SQLSTATE. Stable across versions.