gson uses reflection to serialize types, including standard library types, which are not guaranteed to have the same fields from one release to another. Presuma

gson uses reflection to serialize types, including standard library types, which are not guaranteed to have the same fields from one release to another. Presumably the people who write the jdk realized this potential source of bugs and tried to prevent it from happening, meaning fewer ambiguities about what changes are breaking at the expense of breaking gson (and probably others). see: https://github.com/google/gson/issues/1216 https://github.com/google/gson/issues/1216