fix: is null sql statement (#4690)

* fix is null sql statement

* use == since linter complains about is_

* [autofix.ci] apply automated fixes

* ignore error

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Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

src/backend/base/langflow/services/database/service.py

@@ -152,7 +152,8 @@ class DatabaseService(Service):
         settings_service = get_settings_service()
         if settings_service.auth_settings.AUTO_LOGIN:
             async with self.with_async_session() as session:
-                stmt = select(models.Flow).where(models.Flow.user_id is None)
+                # `== None` translates to SQL `is NULL`
+                stmt = select(models.Flow).where(models.Flow.user_id == None)  # noqa: E711
                 flows = (await session.exec(stmt)).all()
                 if flows:
                     logger.debug("Migrating flows to default superuser")