Set prefs field in user table to null (#1484386)

SQL/mysql.initial.sql

@@ -92,7 +92,7 @@ CREATE TABLE `users` (
   `created` datetime NOT NULL default '0000-00-00 00:00:00',
   `last_login` datetime NOT NULL default '0000-00-00 00:00:00',
   `language` varchar(5) NOT NULL default 'en',
-  `preferences` text NOT NULL default '',
+  `preferences` text,
   PRIMARY KEY  (`user_id`)
 );
 

SQL/mysql5.initial.sql

@@ -28,7 +28,7 @@ CREATE TABLE `users` (
  `created` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `last_login` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `language` varchar(5) NOT NULL DEFAULT 'en',
- `preferences` text NOT NULL DEFAULT '',
+ `preferences` text,
  PRIMARY KEY(`user_id`)
 ) TYPE=MYISAM CHARACTER SET utf8 COLLATE utf8_general_ci;