Pydantic Fix `AliasGenerator` handling of `''` alias

The Fix

Fixes the handling of empty string aliases in the AliasGenerator, allowing them to be used correctly.

Based on closed pydantic/pydantic issue #8808 · PR/commit linked

Open PR/Commit

@@ -296,6 +296,15 @@ def push(self, for_type: type[Any]):
 
 
+def _get_first_non_null(a: Any, b: Any) -> Any:
+    """Return the first argument if it is not None, otherwise return the second argument.
+

fix.md

Option A — Apply the official fix\nFixes the handling of empty string aliases in the AliasGenerator, allowing them to be used correctly.\nWhen NOT to use: This fix should not be applied if the application relies on the previous behavior of ignoring empty string aliases.\n\n

Why This Fix Works in Production

Trigger: Users experienced incorrect alias generation when empty string aliases were specified.
Mechanism: The handling of empty string aliases in the AliasGenerator was incorrect, causing unexpected behavior

Why This Breaks in Prod

The handling of empty string aliases in the AliasGenerator was incorrect, causing unexpected behavior
Production symptom (often without a traceback): Users experienced incorrect alias generation when empty string aliases were specified.

Proof / Evidence

GitHub issue: #8808
Fix PR: https://github.com/pydantic/pydantic/pull/8810
Reproduced locally: No (not executed)
Last verified: 2026-02-12
Confidence: 0.60
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.80

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“See https://github.com/pydantic/pydantic/pull/8806#discussion_r1488616617 for more details”

Issue thread · issue description · source

Failure Signature (Search String)

Users experienced incorrect alias generation when empty string aliases were specified.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Users experienced incorrect alias generation when empty string aliases were specified.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Users experienced incorrect alias generation when empty string aliases were specified.

What Broke

Users experienced incorrect alias generation when empty string aliases were specified.

Why It Broke

The handling of empty string aliases in the AliasGenerator was incorrect, causing unexpected behavior

Fix Options (Details)

Option A — Apply the official fix

Fixes the handling of empty string aliases in the AliasGenerator, allowing them to be used correctly.

When NOT to use: This fix should not be applied if the application relies on the previous behavior of ignoring empty string aliases.

Fix reference: https://github.com/pydantic/pydantic/pull/8810

Last verified: 2026-02-12. Validate in your environment.

When NOT to Use This Fix

This fix should not be applied if the application relies on the previous behavior of ignoring empty string aliases.

Did This Fix Work in Your Case?

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Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.

Related Issues

No related fixes found.

Cluster: pydantic:other Pydantic hub Pydantic best practices All hubs All clusters

Related clusters: Configuration error Data consistency OpenAPI schema

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Pydantic Fix `AliasGenerator` handling of `''` alias specifications (Fix)