There are two versions of Null Pointer out there in the wild. The only official version is the one by Johnny Batch. If you get one by Ken McConnell, it is no longer supported by GB Press. There are still some of those Code Ball cover versions available both in ebook and paperback, but they are inferior First Editions that are full of errors.
The new version by Johnny Batch is far better and cheaper in paperback at $9.95 and only $2.99 for the ebook. You can get the ebooks for Kindle, Nook and from Smashwords in other formats. It is not for sale in the Apple Store or Kobo. If you want an open version of the .epub, get it from Nook.