In JRuby 1.7.5 dev, DateTime.new(0) raises an ArgumentError and indicates it is an invalid date. This same invocation works fine in JRuby 1.7.4 and MRI 2.0.0-p247. My guess is the Joda-Time changes that made their way into 1.7.5 recently are the cause.

I can work around this in my app for now, but it seems an exception shouldn't be raised. As for a use case, I use this (clearly old) date is used as a null object for sorting operations.