Not all code paths return a value - where?

Question

I have the following C# code. For reasons I won\'t go into, this is the required way of localising.

My problem is, I cannot for the life of me figure out what path is no

Answer 1

What is the purpose of the if-block? As far a I can see, if code below the switch is executed, StringNotFound will always be true so the if-block is not necessary, but it may very well confuse the code analysis.