FindBugs.java

import edu.umd.cs.findbugs.annotations.*;

public class FindBugs {

    @CheckForNull
    Object getNull() {
        return null;
    }

    @NonNull MyList<@org.checkerframework.checker.nullness.qual.Nullable Object> getListOfNulls() {
        //:: error: (return.type.incompatible)
        return null; // error
    }

    void test() {
        Object o = getNull();
        //:: error: (dereference.of.nullable)
        o.toString(); // error

        MyList<@org.checkerframework.checker.nullness.qual.Nullable Object> l = getListOfNulls();
        l.toString();
        //:: error: (dereference.of.nullable)
        l.get().toString(); // error
    }
}

class MyList<T extends @org.checkerframework.checker.nullness.qual.Nullable Object> {
    T get() {
        throw new RuntimeException();
    }
}