我已经验证了注册表中的自定义字段，我读取了wordpress的codex，所以我自己也是这样做的。但我发现它会抛出像这样的错误

Call to a member function add() on a non-object  I don\'t know why this should happen. How can i overcome this. 

Code:

function myplugin_check_fields($errors, $sanitized_user_login, $user_email) {

        $errors->add( \'demo_error\', __(\'<strong>ERROR</strong>: This is a demo error. Registration halted.\',\'mydomain\') );

        return $errors;

    }

    add_filter(\'registration_errors\', \'myplugin_check_fields\', 10, 3);