While reading Head First Design Patterns, I came across the Null Object Pattern. Which, depending on who you ask, may not be a design pattern. Head First Design Patterns refers to the Null Object as a "Pattern Honorable Mention". Here is an excerpt of their description:
"A null object is useful when you don't have a meaningful object to return, and yet you want to remove responsibility for handling null from the client."
For an excellent description with examples, check out this explanation by Jeremy Jarrel (or at least I think that's his/her name...the only place I could find something that looked like the author's name was in the domain, but I didn't look too hard).