AssertNonNullTest.java

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

public class AssertNonNullTest {
    public @Nullable String s;

    //:: error: (contracts.postcondition.not.satisfied)
    public @EnsuresNonNull("s") void makeNN() {
        s = null;
    }

    public static void main(String[] args) {
        AssertNonNullTest a = new AssertNonNullTest();
        //:: error: (dereference.of.nullable)
        a.s.equals("we");
        AssertNonNullTest b = new AssertNonNullTest();
        b.makeNN();
        b.s.equals("we");
    }
}