#vulnerable code 
                                @Override
    protected void process(ComplexEventChunk<StreamEvent> streamEventChunk, Processor nextProcessor, StreamEventCloner streamEventCloner) {
        while (streamEventChunk.hasNext()) {
            StreamEvent streamEvent = streamEventChunk.next();
            StreamEvent clonedEvent = streamEventCloner.copyStreamEvent(streamEvent);
            clonedEvent.setType(StreamEvent.Type.EXPIRED);
            if (count < length) {
                count++;
                this.expiredEventChunk.add(clonedEvent);
            } else {
                StreamEvent firstEvent = this.expiredEventChunk.poll();
                streamEventChunk.insertBeforeCurrent(firstEvent);
                this.expiredEventChunk.add(clonedEvent);
            }
        }
        nextProcessor.process(streamEventChunk);
    } 
                            #location 12 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    protected void process(ComplexEventChunk<StreamEvent> streamEventChunk, Processor nextProcessor, StreamEventCloner streamEventCloner) {
        while (streamEventChunk.hasNext()) {
            StreamEvent streamEvent = streamEventChunk.next();
            StreamEvent clonedEvent = streamEventCloner.copyStreamEvent(streamEvent);
            clonedEvent.setType(StreamEvent.Type.EXPIRED);
            if (count < length) {
                count++;
                this.expiredEventChunk.add(clonedEvent);
            } else {
                StreamEvent firstEvent = this.expiredEventChunk.poll();
                if(firstEvent!=null) {
                    streamEventChunk.insertBeforeCurrent(firstEvent);
                    this.expiredEventChunk.add(clonedEvent);
                }
                else {
                    streamEventChunk.insertBeforeCurrent(clonedEvent);
                }
            }
        }
        nextProcessor.process(streamEventChunk);
    }