fix mypy failure

Change-Id: I33769e9ef98a0f35d7429cd63c857b98298161be

diff --git a/alembic/ddl/mssql.py b/alembic/ddl/mssql.py
index 5376da5adece8799051c35126bbddcf938acef0f..50d441f8be1f5590c3ba014e97300ac767c4603b 100644 (file)
--- a/alembic/ddl/mssql.py
+++ b/alembic/ddl/mssql.py
@@ -96,7 +96,9 @@ class MSSQLImpl(DefaultImpl):
         type_: Optional[TypeEngine] = None,
         schema: Optional[str] = None,
         existing_type: Optional[TypeEngine] = None,
-        existing_server_default: Optional[_ServerDefault] = None,
+        existing_server_default: Union[
+            _ServerDefault, Literal[False], None
+        ] = None,
         existing_nullable: Optional[bool] = None,
         **kw: Any,
     ) -> None: