几个选择；首先，您要启用`ACCEPT_EMPTY_STRING_AS_NULL_OBJECT’：
mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
so that empty String becomes null. And if you want it to get converted to
actual empty List, override setter:
public void setChildren(List<Child> c) { if (c == null) { children = Collections.emptyList(); } else { chidlren = c; }}
