c# ? operator
?? Operator (C# Reference) – MSDN – Microsoft
Simple Example Usages
Several folks have blogged about the ?? operator in the past – read here, here, here, and here for some previous examples on how to use it. Simply put, the ?? operator checks whether the value provided on the left side of the expression is null, and if so it returns an alternate value indicated by the right side of the expression. If the value provided on the left side of the expression isn’t null, then it returns the original value.
For example, let’s assume we have a string variable “message”. We could check whether message was null, and return an alternate value using the code below:
Because the “message” variable above wasn’t null, the “result” variable is assigned the original “hello world” message value.