getStagedApexInfo() returns @nullable

Its return value (StagedApexInfo) is nullable, but not in .aidl file.
This doesn't affect in the Java backend, but it matters in the other
native backends including Rust.

Bug: 199146189
Test: m
Change-Id: Idab01ad1989100293e03cd7c2c605eb2d51f2e88
1 file changed