I cann‘t create a new epub files because of null pointer exception

[IceSakuraAzure]

this is my code:

       EpubReader epubReader = new EpubReader();
       String filePath="src/example/test.epub";
       File file=new File(filePath);
       InputStream input = null ;
       input = new FileInputStream(file);
       Book book=epubReader.readEpub(input,"UTF-8");
       Spine spine = book.getSpine();
       List<SpineReference> spineReferences = spine.getSpineReferences();
       int i = 0;
       if (spineReferences != null && spineReferences.size() > 0) {
           System.out.println("Converting...");
           for (i = 0; i < spineReferences.size(); i++) {
           	dealResource(i,spineReferences.get(i).getResource());//change some text in every Resource  
   	    }
           System.out.println("Convert End,Total chapters:"+i);
       }else{
           System.out.println("EpubBook is null");
           System.exit(0);
       }               
       EpubWriter epubWriter = new EpubWriter();
       epubWriter.write(book, new FileOutputStream("src/example/test-t2s.epub"));

but when I run it,it throw a exception:

Convert End,Total chapters:751
Exception in thread "main" java.lang.NullPointerException
	at nl.siegmann.epublib.epub.PackageDocumentWriter.write(PackageDocumentWriter.java:36)
	at nl.siegmann.epublib.epub.EpubWriter.writePackageDocument(EpubWriter.java:112)
	at nl.siegmann.epublib.epub.EpubWriter.write(EpubWriter.java:53)
	at com.blue.core.convertMain.readbook(convertMain.java:75)
	at com.blue.core.convertMain.main(convertMain.java:49)

I don't know what happend.The test-t2s.epub is created,but it's broken.I use winRAR to open the epub files,and I find the content.opt only 0KB.WinRAR also warning me the content.opt is broken.
I want to know how to deal this problem.
My project depends this jar:
xmlpull-1.1.3.4d_b4_min.jar,epublib-core-3.1.3.jar,slf4j-api-1.7.2.jar,kxml2-2.3.0 and so on.I find these in Maven.com