Contao\Database\Updater::run35Update PHP Method

    public function run35Update()
    {
        $this->Database->query("ALTER TABLE `tl_member` CHANGE `username` `username` varchar(64) COLLATE utf8_bin NULL");
        $this->Database->query("UPDATE `tl_member` SET username=NULL WHERE username=''");
        $this->Database->query("ALTER TABLE `tl_member` DROP INDEX `username`, ADD UNIQUE KEY `username` (`username`)");
    }