Validation of null in a switch-case with pattern matching does not work as expected.

[pompiuses]

Environment:
NullAway version: 0.10.23
Java 21 on Mac M1

I've got the following code:

public class OnsetValidator {
    public static Optional<FhirProfileValidationError> validateOnset(@Nullable Type onset) {
        return switch (onset) {
            case null -> Optional.empty(); // Null is validated here.
            case DateTimeType d -> validateOnsetDate(d);
            case Age a -> validateOnsetAge(a);
            // NullAway complains in default: OnsetValidator.java:[17,97] [NullAway] dereferenced expression onset is @Nullable
            default -> Optional.of(new FhirProfileValidationError("Invalid onset type: " + onset.getClass().getName()));
        };
    }

    private static Optional<FhirProfileValidationError> validateOnsetAge(Age a) {
        return Optional.empty(); // Some validation.
    }

    private static Optional<FhirProfileValidationError> validateOnsetDate(DateTimeType d) {
        return Optional.empty(); // Some validation.
    }
}

Even though null is validated in the switch, NullAway gives an error for the default case. I assume this is a bug?

[msridhar]

Yes I believe there is a bug here. What should happen is that since there is a case null, NullAway should learn that onset cannot be null in the default case.

I'll look into this, but it's possible a fix is blocked on google/error-prone#4119.