I encountered some code today that appears to be exposing a bug in the NullReference analysis in ReSharper 2.5.1. I have attached a screenshot of the code with the possible NullReference warnings. You will notice, that if the urlString parameter is null, then the length variable will be 0, and thus the for loop block will never be entered.
I concede that this is a rather complicated case, but I thought it was worth posting. This code was actually ripped out of a private method in the System.Web.dll assembly by using the dotNet Reflector.