#fixed code
                                public long exceptsPerCycle(int cycle) {
        StoreTailer tailer = acquireTailer();
        try {
            long index = rollCycle.toIndex(cycle, 0);
            if (tailer.moveToIndex(index)) {
                assert tailer.store != null && tailer.store.refCount() > 0;
                return tailer.store.lastSequenceNumber(tailer) + 1;
            } else {
                return -1;
            }
        } catch (StreamCorruptedException e) {
            throw new IllegalStateException(e);
        } finally {
            tailer.release();
        }
    }
#vulnerable code 
                                public long exceptsPerCycle(int cycle) {
        StoreTailer tailer = acquireTailer();
        try {
            long index = rollCycle.toIndex(cycle, 0);
            if (tailer.moveToIndex(index)) {
                assert tailer.store.refCount() > 0;
                return tailer.store.lastSequenceNumber(tailer) + 1;
            } else {
                return -1;
            }
        } catch (StreamCorruptedException e) {
            throw new IllegalStateException(e);
        } finally {
            tailer.release();
        }
    } 
                            #location 6 
                            #vulnerability type NULL_DEREFERENCE