Different treatment for ?: and if...else in dataflow refinement

[mernst]

Consider the following code. The two classes ImmutableIntList1 and ImmutableIntList2 have the same logic and control flow, but the Nullness Checker issues an error message for the first but not the second:

Issue3622.java:14: error: [contracts.conditional.postcondition.not.satisfied] conditional postcondition is not satisfied when equals returns true.
            return obj instanceof ImmutableIntList1 ? true : obj instanceof List;
            ^
  found   : obj is @Nullable
  required: obj is @NonNull

// Test case for https://tinyurl.com/cfissue/3622

// @skip-test until the issue is fixed

import java.util.List;
import org.checkerframework.checker.nullness.qual.Nullable;

public class Issue3622 {

    public class ImmutableIntList1 {

        @Override
        public boolean equals(@Nullable Object obj) {
            return obj instanceof ImmutableIntList1 ? true : obj instanceof List;
        }
    }

    public class ImmutableIntList2 {

        @Override
        public boolean equals(@Nullable Object obj) {
            if (obj instanceof ImmutableIntList2) {
                return true;
            } else {
                return obj instanceof List;
            }
        }
    }
}