hub: editTagExternalRepo is able to set merge_mode

fixes: #1857

docs/schema-upgrade-1.20-1.21.sql

@@ -13,4 +13,8 @@ CREATE OR REPLACE FUNCTION get_event() RETURNS INTEGER AS '
     SELECT currval(''events_id_seq'')::INTEGER;
 ' LANGUAGE SQL;
 
+-- merge_mode can not be null
+UPDATE tag_external_repos SET merge_mode = 'koji' WHERE merge_mode is NULL;
+ALTER TABLE tag_external_repos ALTER COLUMN merge_mode SET NOT NULL;
+
 COMMIT;

docs/schema.sql

@@ -484,7 +484,7 @@ create table tag_external_repos (
 	tag_id INTEGER NOT NULL REFERENCES tag(id),
 	external_repo_id INTEGER NOT NULL REFERENCES external_repo(id),
 	priority INTEGER NOT NULL,
-	merge_mode TEXT DEFAULT 'koji',
+	merge_mode TEXT NOT NULL DEFAULT 'koji',
 -- versioned - see earlier description of versioning
 	create_event INTEGER NOT NULL REFERENCES events(id) DEFAULT get_event(),
 	revoke_event INTEGER REFERENCES events(id),