This matches the Java extractor's treatment of these literals, and so enables dataflow type-tracking to avoid special-casing Kotlin. Natively, Kotlin would regard this as kotlin.Nothing?, the type that can only contain null (kotlin.Nothing without a ? can take nothing at all), which gets Java-ified as java.lang.Void, and this will continue to be used when a null type has to be "boxed", as in representing substituted generic constraints with no possible type.