apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/txtresolver/PropertyResolver.java/PropertyResolver/deleteCommentAndBlankItem
class PropertyResolver:  private void deleteCommentAndBlankItem(Map<Integer, ItemDTO> oldLineNumMapItem,
                                         Map<Integer, String> newLineNumMapItem,
                                         ItemChangeSets changeSets) {

    for (Map.Entry<Integer, ItemDTO> entry : oldLineNumMapItem.entrySet()) {
      int lineNum = entry.getKey();
      ItemDTO oldItem = entry.getValue();
      String newItem = newLineNumMapItem.get(lineNum);

      //1. old is blank by now is not
      //2.old is comment by now is not exist or modified
      if ((isBlankItem(oldItem) && !isBlankItem(newItem))
          || isCommentItem(oldItem) && (newItem == null || !newItem.equals(oldItem.getComment()))) {
        changeSets.addDeleteItem(oldItem);
      }
    }
  }