public function getUsername()
    {
        if (!$this->hasEnabledUsername()) {
            return null;
        }
        $usernameClass = $this->usernameClass;
        $noInit = $usernameClass::buildNoInitModel();
        /* @var $noInit Username */
        return $this->hasOne($usernameClass, [$noInit->createdByAttribute => $this->guidAttribute]);
    }