#vulnerable code 
                                public WriteResult<T, K> update(T query, T object, boolean upsert, boolean multi, WriteConcern concern) throws MongoException {
        return update(convertToDbObject(query), convertToDbObject(object), upsert, multi, concern);
    } 
                            #location 2 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public WriteResult<T, K> update(T query, T object, boolean upsert, boolean multi, WriteConcern concern) throws MongoException {
        return update(convertToBasicDbObject(query), convertToBasicDbObject(object), upsert, multi, concern);
    }