generateKotlinNullableClasses should still generate nice toString for objects

[JLLeitschuh]

When using generateKotlinNullableClasses, it becomes impossible to use toString in the debugger to view the full scope of all the fields that were actually accessed.

It would be nice if the generated functions held information whether or not the field were present or not, that way, a sane toString could be generated that checks if each field were present before adding it to the printed string.