/**
  * 
  * @param DOMDocument $xml
  * @return NULL|WpProQuiz_Model_Question
  */
 private function createQuestionModel($xml)
 {
     $model = new WpProQuiz_Model_Question();
     $model->setTitle(trim($xml->title));
     $model->setQuestion(trim($xml->questionText));
     $model->setCorrectMsg(trim($xml->correctMsg));
     $model->setIncorrectMsg(trim($xml->incorrectMsg));
     $model->setAnswerType(trim($xml->attributes()->answerType));
     $model->setCorrectSameText($xml->correctSameText == 'true');
     $model->setTipMsg(trim($xml->tipMsg));
     if (isset($xml->tipMsg) && $xml->tipMsg->attributes() !== null) {
         $model->setTipEnabled($xml->tipMsg->attributes()->enabled == 'true');
     }
     $model->setPoints($xml->points);
     $model->setShowPointsInBox($xml->showPointsInBox == 'true');
     $model->setAnswerPointsActivated($xml->answerPointsActivated == 'true');
     $model->setAnswerPointsDiffModusActivated($xml->answerPointsDiffModusActivated == 'true');
     $model->setDisableCorrect($xml->disableCorrect == 'true');
     $model->setCategoryName(trim($xml->category));
     $answerData = array();
     if (isset($xml->answers)) {
         foreach ($xml->answers->answer as $answer) {
             $answerModel = new WpProQuiz_Model_AnswerTypes();
             $attr = $answer->attributes();
             if ($attr !== null) {
                 $answerModel->setCorrect($attr->correct == 'true');
                 $answerModel->setPoints($attr->points);
             }
             $answerModel->setAnswer(trim($answer->answerText));
             if ($answer->answerText->attributes() !== null) {
                 $answerModel->setHtml($answer->answerText->attributes()->html);
             }
             $answerModel->setSortString(trim($answer->stortText));
             if ($answer->stortText->attributes() !== null) {
                 $answerModel->setSortStringHtml($answer->stortText->attributes()->html);
             }
             $answerData[] = $answerModel;
         }
     }
     $model->setAnswerData($answerData);
     //Check
     if (trim($model->getAnswerType()) == '') {
         return null;
     }
     if (trim($model->getQuestion()) == '') {
         return null;
     }
     if (trim($model->getTitle()) == '') {
         return null;
     }
     if (count($model->getAnswerData()) == 0) {
         return null;
     }
     return $model;
 }