build method Null safety

Implementation

@override
Widget build(BuildContext context) {
  if (knowledgePanel.titleElement == null) {
    return EMPTY_WIDGET;
  }
  switch (knowledgePanel.titleElement!.type) {
    case TitleElementType.GRADE:
      return Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: <Widget>[
          ScoreCard(
            iconUrl: knowledgePanel.titleElement!.iconUrl,
            description: knowledgePanel.titleElement!.title,
            cardEvaluation: getCardEvaluationFromKnowledgePanelTitleElement(
              knowledgePanel.titleElement!,
            ),
          ),
        ],
      );
    case null:
    case TitleElementType.UNKNOWN:
      return KnowledgePanelTitleCard(
        knowledgePanelTitleElement: knowledgePanel.titleElement!,
        evaluation: knowledgePanel.evaluation,
      );
  }
}