apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/txtresolver/PropertyResolver.java/PropertyResolver/handleCommentLine
class PropertyResolver:  private void handleCommentLine(Long namespaceId, ItemDTO oldItemByLine, String newItem, int lineCounter, ItemChangeSets changeSets) {
    String oldComment = oldItemByLine == null ? "" : oldItemByLine.getComment();
    //create comment. implement update comment by delete old comment and create new comment
    if (!(isCommentItem(oldItemByLine) && newItem.equals(oldComment))) {
      changeSets.addCreateItem(buildCommentItem(0L, namespaceId, newItem, lineCounter));
    }
  }