Fix: ensure bool(check_query_exists) returns True or False

airflow/utils/db.py

@@ -1458,7 +1458,8 @@ def check_query_exists(query_stmt: Select, *, session: Session) -> bool:
     :meta private:
     """
     count_stmt = select(literal(True)).select_from(query_stmt.order_by(None).subquery())
-    return session.scalar(count_stmt)
+    # we must cast to bool because scalar() can return None
+    return bool(session.scalar(count_stmt))
 
 
 def exists_query(*where: ClauseElement, session: Session) -> bool:

tests/utils/test_db.py

@@ -32,11 +32,12 @@
 from alembic.migration import MigrationContext
 from alembic.runtime.environment import EnvironmentContext
 from alembic.script import ScriptDirectory
-from sqlalchemy import MetaData
+from sqlalchemy import Column, Integer, MetaData, Table, select
 
 from airflow.models import Base as airflow_base
 from airflow.settings import engine
 from airflow.utils.db import (
+    LazySelectSequence,
     _get_alembic_config,
     check_migrations,
     compare_server_default,
@@ -251,3 +252,16 @@ def test_alembic_configuration(self):
         import airflow
 
         assert config.config_file_name == os.path.join(os.path.dirname(airflow.__file__), "alembic.ini")
+
+    def test_bool_lazy_select_sequence(self):
+        class MockSession:
+            def __init__(self):
+                pass
+
+            def scalar(self, stmt):
+                return None
+
+        t = Table("t", MetaData(), Column("id", Integer, primary_key=True))
+        lss = LazySelectSequence.from_select(select(t.c.id), order_by=[], session=MockSession())
+
+        assert bool(lss) is False