At work we ran into a problem with Mongrel crashing after upgrading to Rails 2.3.11. The errors were:
Tue May 25 20:24:52 +0300 2010: Error calling Dispatcher.dispatch #<NoMethodError: You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.split>
as well as:
The error occurred while evaluating nil.
We found Lighthouse issue #4690 covering the problem. The issue linked to gist: 471663 GitHub with a fix for the problem. The gist contained some comments to resolve some issues, namely an “illformed requirement” error and applying the fix for rails versions other than 2.3.8.
After a bit of tweaking we ended up with an initializer that worked for us.