* [sql] add default value.

db/update22.0.sql

@@ -5,7 +5,7 @@ ALTER TABLE `zt_deliverable` ADD `trimmable` char(30) NOT NULL DEFAULT '0' AFTER
 ALTER TABLE `zt_deliverable` ADD `trimRule` varchar(255) NOT NULL AFTER `trimmable`;
 ALTER TABLE `zt_deliverable` ADD `template` text NOT NULL AFTER `trimRule`;
 ALTER TABLE `zt_deliverable` ADD `status` varchar(30) NOT NULL DEFAULT 'enabled' AFTER `name`;
-ALTER TABLE `zt_deliverable` ADD `category` varchar(255) NULL AFTER `lastEditedDate`;
+ALTER TABLE `zt_deliverable` ADD `category` varchar(255) NOT NULL DEFAULT '' AFTER `lastEditedDate`;
 
 CREATE TABLE IF NOT EXISTS `zt_deliverablestage` (
   `id` int(8) unsigned NOT NULL AUTO_INCREMENT,

db/zentao.sql

@@ -605,7 +605,7 @@ CREATE TABLE `zt_deliverable` (
   `createdDate` date NULL,
   `lastEditedBy` varchar(30) NULL,
   `lastEditedDate` date NULL,
-  `category` varchar(255) NULL,
+  `category` varchar(255) NOT NULL DEFAULT '',
   `deleted` enum('0','1') NOT NULL DEFAULT '0',
   PRIMARY KEY (`id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;