Ouch! Please stop the head banging RIGHT NOW ;-)

More seriously, behavior = code + inputs + environment. So if you are absolutely sure that

• no code changes and even your version control diff command agrees
• no 3rd party library code changes
• no changes to build scripts
• no anything recompiled a slightly different way
• no test suite changes
• the exact same test data worked yesterday
• all test "random" generators are seeded the same way

That pretty much leaves the option that your software is interacting with some part of the environment in ways you do not expect. Either (a) you have always been getting the undef but were traversing the code in a way it didn't matter or (b) some environmental factor is interacting with upstream code causing the undef IP address.

The obvious environmental things to look for are:

• database configuration and contents changes
• Apache server configuration changes
• Environment variables
• Your own profiles (or that of the user under which you are running the tests)
• Any bits of code that interact with the above

Failing that, go out and take a walk, pet the dog, play with the kids, or call a good friend and chat or do something having nothing to do with the problem. More than once, I've gotten myself entirely frustrated with a bug, only to have lunch with a friend, come back, and find the bugger in less than five minutes.

But you know all this, so you can probably go back to your head banging after reading this. Just choose a pillow next time. :-)

Wish I could help more, beth