+On recent Pg versions:
+
+ALTER TABLE svc_forward ALTER COLUMN srcsvc DROP NOT NULL;
+ALTER TABLE h_svc_forward ALTER COLUMN srcsvc DROP NOT NULL;
+ALTER TABLE svc_forward ALTER COLUMN dstsvc DROP NOT NULL;
+ALTER TABLE h_svc_forward ALTER COLUMN dstsvc DROP NOT NULL;
+
+Or on Pg versions that don't support DROP NOT NULL (tested only on 7.2 so far):
+UPDATE pg_attribute SET attnotnull = FALSE WHERE ( attname = 'srcsvc' OR attname = 'dstsvc' ) AND ( attrelid = ( SELECT oid FROM pg_class WHERE relname = 'svc_forward' ) OR attrelid = ( SELECT oid FROM pg_class WHERE relname = 'h_svc_forward' ) );
+