code: private boolean isApply(ChangeSet changeSet) {
          // 必须包含　PENDING_DROPS　不然无法在只删除列时产生变更脚本
          return (changeSet.getType() == ChangeSetType.APPLY || changeSet.getType() == ChangeSetType.PENDING_DROPS)
                  && !changeSet.getChangeSetChildren().isEmpty();
      }
docs: Return true if the changeSet is APPLY and not empty.