Gson can create Kotlin objects with surprisingly null parameters

One of my projects uses Gson to load a bit of state from a JSON file. The state is represented by a Kotlin data class with non-null properties. I expected that instances of this class would fail to initialize if Gson didn't find a JSON property for all the properties, in which case the program would fall back to my default. Instead it created an instance with that non-null-declared property set to null, which produced a confusing stack trace. Checking the property against null works, of course, but Kotlin produces a "senseless comparison" warning.