Pydantic mypy thinks a config variable can never be None

The Fix

pip install pydantic==2.7

Based on closed pydantic/pydantic issue #9068 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -126,10 +126,6 @@ def plugin(version: str) -> type[Plugin]:
 
 
-class _DeferAnalysis(Exception):
-    pass
-

repro.py

import pydantic


class ModelNested(pydantic.BaseModel):
    my_var: str | None = pydantic.Field(default=None)


class Model(ModelNested):
    pass


m = Model()
if m.my_var is None:
    print("hello there")  # test.py:14: error: Statement is unreachable  [unreachable]

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install pydantic==2.7\nWhen NOT to use: Do not apply this fix if using a version of Pydantic prior to 2.7.\n\n

Why This Fix Works in Production

Trigger: print("hello there") # test.py:14: error: Statement is unreachable [unreachable]
Mechanism: Mypy incorrectly infers that a config variable can never be None in inherited BaseModel classes
Why the fix works: Fix handling of optionals in mypy plugin to resolve mypy issues with optional types. (first fixed release: 2.7).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Mypy incorrectly infers that a config variable can never be None in inherited BaseModel classes
Production symptom (often without a traceback): print("hello there") # test.py:14: error: Statement is unreachable [unreachable]

Proof / Evidence

GitHub issue: #9068
Fix PR: https://github.com/pydantic/pydantic/pull/9008
First fixed release: 2.7
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.65

Discussion

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

Jump to Sources Open on GitHub

“Should be fixed in 2.7, coming out soon! Fixed by @dmontagu here: https://github.com/pydantic/pydantic/pull/9008”

@sydney-runkle · 2024-03-22 · confirmation · source

Failure Signature (Search String)

print("hello there") # test.py:14: error: Statement is unreachable [unreachable]

Copy-friendly signature

signature.txt

Failure Signature
-----------------
print("hello there")  # test.py:14: error: Statement is unreachable  [unreachable]
python version: 3.12.2 (main, Feb 14 2024, 11:13:34) [Clang 15.0.0 (clang-1500.1.0.2.5)]

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
print("hello there")  # test.py:14: error: Statement is unreachable  [unreachable]
python version: 3.12.2 (main, Feb 14 2024, 11:13:34) [Clang 15.0.0 (clang-1500.1.0.2.5)]

Minimal Reproduction

repro.py

import pydantic


class ModelNested(pydantic.BaseModel):
    my_var: str | None = pydantic.Field(default=None)


class Model(ModelNested):
    pass


m = Model()
if m.my_var is None:
    print("hello there")  # test.py:14: error: Statement is unreachable  [unreachable]

Environment

Pydantic: 2

What Broke

Mypy reports unreachable code errors when checking optional variables in models.

Why It Broke

Mypy incorrectly infers that a config variable can never be None in inherited BaseModel classes

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install pydantic==2.7

When NOT to use: Do not apply this fix if using a version of Pydantic prior to 2.7.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/pydantic/pydantic/pull/9008

First fixed release: 2.7

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

Do not apply this fix if using a version of Pydantic prior to 2.7.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

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.

Version Compatibility Table

Version	Status
2.7	Fixed

Related Issues

No related fixes found.

Cluster: pydantic:configuration-error Pydantic hub Pydantic best practices All hubs All clusters

Related clusters: Data consistency OpenAPI schema Serialization

Sources

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

Pydantic mypy thinks a config variable can never be None when nested in inherited BaseModel class, (Fix)