output: #fixed code
                                  @Test
      public void testObjectIdSaved() {
          ObjectIdId object = new ObjectIdId();
          org.bson.types.ObjectId id = new org.bson.types.ObjectId();
          object._id = id;
  
          JacksonDBCollection<ObjectIdId, org.bson.types.ObjectId> coll = getCollection(ObjectIdId.class,
                  org.bson.types.ObjectId.class);
  
          coll.insert(object);
          ObjectIdId result = coll.findOneById(id);
          assertThat(result._id, equalTo(id));
          assertThat((org.bson.types.ObjectId) coll.getDbCollection().findOne().get("_id"), equalTo(id));
      }
input: #vulnerable code 
                                  @Test
      public void testObjectIdSaved() {
          ObjectIdId object = new ObjectIdId();
          org.bson.types.ObjectId id = new org.bson.types.ObjectId();
          object._id = id;
  
          JacksonDBCollection<ObjectIdId, org.bson.types.ObjectId> coll = getCollection(ObjectIdId.class,
                  org.bson.types.ObjectId.class);
  
          coll.insert(object);
          ObjectIdId result = coll.findOneById(id);
          assertThat(result._id, equalTo(id));
      } 
                              #location 12 
                              #vulnerability type NULL_DEREFERENCE