apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/utils/ConfigChangeContentBuilder.java/ConfigChangeContentBuilder/deleteItem
class ConfigChangeContentBuilder:  public ConfigChangeContentBuilder deleteItem(Item item) {
    if (!StringUtils.isEmpty(item.getKey())) {
      deleteItems.add(cloneItem(item));
    }
    return this;
  }