#vulnerable code 
                                private void advanceCommitIndex(RaftMessage.AppendEntriesRequest request) {
        long newCommitIndex = Math.min(request.getCommitIndex(),
                request.getPrevLogIndex() + request.getEntriesCount());
        raftNode.setCommitIndex(newCommitIndex);
        if (raftNode.getLastAppliedIndex() < raftNode.getCommitIndex()) {
            // apply state machine
            for (long index = raftNode.getLastAppliedIndex() + 1;
                 index <= raftNode.getCommitIndex(); index++) {
                RaftMessage.LogEntry entry = raftNode.getRaftLog().getEntry(index);
                if (entry.getType() == RaftMessage.EntryType.ENTRY_TYPE_DATA) {
                    raftNode.getStateMachine().apply(entry.getData().toByteArray());
                } else if (entry.getType() == RaftMessage.EntryType.ENTRY_TYPE_CONFIGURATION) {
                    raftNode.applyConfiguration(entry);
                }
                raftNode.setLastAppliedIndex(index);
            }
        }
    } 
                            #location 10 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                private void advanceCommitIndex(RaftMessage.AppendEntriesRequest request) {
        long newCommitIndex = Math.min(request.getCommitIndex(),
                request.getPrevLogIndex() + request.getEntriesCount());
        raftNode.setCommitIndex(newCommitIndex);
        if (raftNode.getLastAppliedIndex() < raftNode.getCommitIndex()) {
            // apply state machine
            for (long index = raftNode.getLastAppliedIndex() + 1;
                 index <= raftNode.getCommitIndex(); index++) {
                RaftMessage.LogEntry entry = raftNode.getRaftLog().getEntry(index);
                if (entry != null) {
                    if (entry.getType() == RaftMessage.EntryType.ENTRY_TYPE_DATA) {
                        raftNode.getStateMachine().apply(entry.getData().toByteArray());
                    } else if (entry.getType() == RaftMessage.EntryType.ENTRY_TYPE_CONFIGURATION) {
                        raftNode.applyConfiguration(entry);
                    }
                }
                raftNode.setLastAppliedIndex(index);
            }
        }
    }