关于xstream的错误 it does not have a no-args constructor

Exception in thread "main" com.thoughtworks.xstream.converters.ConversionException

Cannot construct ddd.ajava.chapter7.question2.Address as it does not have a no-args constructor :

Cannot construct ddd.ajava.chapter7.question2.Address as it does not have a no-args constructor

如图所示：

解决方法：给错误的类添加无参构造方法。

（记录踩过的坑）