#vulnerable code 
                              private static void checkFollowerCommitLagsLeader(MiniRaftCluster cluster) {
    List<RaftServerImpl> followers = cluster.getFollowers();
    RaftServerImpl leader = cluster.getLeader();

    RatisMetricRegistry leaderMetricsRegistry =
        RatisMetrics.getMetricRegistryForRaftLeader(
            leader.getMemberId().toString());

    Gauge leaderCommitGauge = RaftLeaderMetrics
        .getPeerCommitIndexGauge(leader, leader);

    for (RaftServerImpl follower : followers) {
      Gauge followerCommitGauge = RaftLeaderMetrics
          .getPeerCommitIndexGauge(leader, follower);
      Assert.assertTrue((Long)leaderCommitGauge.getValue() >=
          (Long)followerCommitGauge.getValue());
    }
  } 
                            #location 7 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              private static void checkFollowerCommitLagsLeader(MiniRaftCluster cluster) {
    List<RaftServerImpl> followers = cluster.getFollowers();
    RaftServerImpl leader = cluster.getLeader();

    Gauge leaderCommitGauge = RaftServerMetrics
        .getPeerCommitIndexGauge(leader, leader);

    for (RaftServerImpl follower : followers) {
      Gauge followerCommitGauge = RaftServerMetrics
          .getPeerCommitIndexGauge(leader, follower);
      Assert.assertTrue((Long)leaderCommitGauge.getValue() >=
          (Long)followerCommitGauge.getValue());
      Gauge followerMetric = RaftServerMetrics
          .getPeerCommitIndexGauge(follower, follower);
      System.out.println(followerCommitGauge.getValue());
      System.out.println(followerMetric.getValue());
      Assert.assertTrue((Long)followerCommitGauge.getValue()  <= (Long)followerMetric.getValue());
    }
  }