By the nature of non-static inner classes, they cannot have a default non-argument constructor which makes not possible to deserialize them using default mapping. The spec has to be changed in a way that non-static inner classes support is removed or non-static inner classes are supported only for serialization.
See discussion on Yasson issues tracker:
https://github.com/eclipse/yasson/issues/49
By the nature of non-static inner classes, they cannot have a default non-argument constructor which makes not possible to deserialize them using default mapping. The spec has to be changed in a way that non-static inner classes support is removed or non-static inner classes are supported only for serialization. See discussion on Yasson issues tracker: https://github.com/eclipse/yasson/issues/49