#vulnerable code 
                                @Override
    public List<ReferenceTypeUsage> getAllAncestors() {
        List<ReferenceTypeUsage> ancestors = new LinkedList<>();
        if (getSuperClass(typeSolver) != null) {
            ancestors.add(new ReferenceTypeUsage(getSuperClass(typeSolver), typeSolver));
            ancestors.addAll(getSuperClass(typeSolver).getAllAncestors());
        }
        ancestors.addAll(getAllInterfaces(typeSolver).stream().map((i)->new ReferenceTypeUsage(i, typeSolver)).collect(Collectors.<ReferenceTypeUsage>toList()));
        return ancestors;
    } 
                            #location 5 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public List<ReferenceTypeUsage> getAllAncestors() {
        List<ReferenceTypeUsage> ancestors = new LinkedList<>();
        if (getSuperClass(typeSolver) != null) {
            ReferenceTypeUsage superClass = getSuperClass(typeSolver);
            ancestors.add(superClass);
            ancestors.addAll(getSuperClass(typeSolver).getAllAncestors());
        }
        ancestors.addAll(getAllInterfaces(typeSolver).stream().map((i)->new ReferenceTypeUsage(i, typeSolver)).collect(Collectors.<ReferenceTypeUsage>toList()));
        return ancestors;
    }