do not fail when compare_server_default compares None values

diff --git a/alembic/ddl/postgresql.py b/alembic/ddl/postgresql.py
index fedaf102ab3dec32744b8ac4ca4c46417c990025..1f146789a3b7d28f667597a4aa531555b59ca8be 100644 (file)
--- a/alembic/ddl/postgresql.py
+++ b/alembic/ddl/postgresql.py
@@ -17,6 +17,9 @@ class PostgresqlImpl(DefaultImpl):
 
         conn_col_default = inspector_column['default']
 
+        if None in (conn_col_default, rendered_metadata_default):
+            return conn_col_default != rendered_metadata_default
+
         if metadata_column.type._type_affinity is not sqltypes.String:
             rendered_metadata_default = re.sub(r"^'|'$", "", rendered_metadata_default)