#vulnerable code 
                                @Test
    public void testCreatorGetterObjectIdAnnotated() throws Exception {
        CreatorGetterObjectIdAnnotated o = new CreatorGetterObjectIdAnnotated(null);
        JacksonDBCollection<CreatorGetterObjectIdAnnotated, String> coll = createCollFor(o, String.class);
        WriteResult<CreatorGetterObjectIdAnnotated, String> writeResult = coll.insert(o);
        assertThat(writeResult.getSavedId(), notNullValue());
        assertThat(writeResult.getSavedId(), instanceOf(String.class));
        assertThat(writeResult.getDbObject().get("id"), nullValue());
        assertThat(writeResult.getSavedId(), equalTo(writeResult.getDbObject().get("_id").toString()));
        CreatorGetterObjectIdAnnotated result = coll.findOneById(writeResult.getSavedId());
        assertThat(result, notNullValue());
        assertThat(result.getId(), equalTo(writeResult.getSavedId()));
    } 
                            #location 12 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void testCreatorGetterObjectIdAnnotated() throws Exception {
        CreatorGetterObjectIdAnnotated o = new CreatorGetterObjectIdAnnotated(new org.bson.types.ObjectId().toString());
        JacksonDBCollection<CreatorGetterObjectIdAnnotated, String> coll = createCollFor(o, String.class);
        coll.insert(o);
        CreatorGetterObjectIdAnnotated result = coll.findOneById(o.id);
        assertThat(result, notNullValue());
        assertThat(result.getId(), equalTo(o.id));
    }