OverrideNNOE.java

import org.checkerframework.checker.nullness.qual.*;
import org.checkerframework.checker.nullness.qual.RequiresNonNull;

class OverrideNNOE {
    static class Super {
        @Nullable Object f;

        void call() {}
    }

    static class Sub extends Super {
        @Override
        @RequiresNonNull("f")
        //:: error: (contracts.precondition.override.invalid)
        void call() {
            f.hashCode();
        }
    }

    public static void main(String[] args) {
        Super s = new Sub();
        s.call();
    }
}