Those of you who read the beta version of Metaprogramming Ruby already know Bill, the grumpy old Ruby mentor. If you didn't get enough of him yet, here's a treat for you.
The January 2010 issue of PragPub magazine contains a short article where Bill lectures you about the ins and outs of Ruby's nil value. In this article, I also introduce a couple of spells that fell on the cutting room floor as I struggled to make the book shorter: the Null Object spell and the Black Hole spell.
You can download PragPub for free (in formats suited for Kindles, iPhones and plain old-fashioned computers). Enjoy!