Apology of the NULL pointer
labs.trolltech.com
labs.trolltech.com
One example I can think of: BeautifulSoup. If no search results are found within the document, it returns None or something similar.
And when that happens somewhere in a whole chain of queries, you're ending up with an exception.
This shouldn't happen ... I want the result of the whole chain queries to be NULL, and I don't care which link in that chain started it.
So languages with Monad comprehensions (or dynamic OOP languages where you can override the runtime dispatching) ... have an advantage here because you can use the Maybe monad.