Use None isntead of sql.null

atst/models/utils.py

@@ -33,4 +33,4 @@ def claim_for_update(resource, minutes=30):
     finally:
         db.session.query(Model).filter(Model.id == resource.id).filter(
             Model.claimed_until != None
-        ).update({"claimed_until": sql.null()}, synchronize_session="fetch")
+        ).update({"claimed_until": None}, synchronize_session="fetch")

tests/test_jobs.py

@@ -288,4 +288,10 @@ def test_claim_for_update(session):
     t1.join()
     t2.join()
 
+    session.refresh(environment)
+
+    # Only FirstThread acquired a claim and wrote to satisfied_claims
     assert satisfied_claims == ["FirstThread"]
+
+    # The claim is released as soon as work is done
+    assert environment.claimed_until is None