#vulnerable code 
                                static UpdateKeeper getInstance() {
        if (singleton == null) {
            synchronized (UpdateKeeper.class) {
                if (singleton == null) {
                    singleton = new UpdateKeeper();
                    return singleton;
                }
            }
        }
        return singleton;
    } 
                            #location 6 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                static UpdateKeeper getInstance() {
        return UpdateKeeper.Builder.singleton;
    }