C# 5.0 Unleashed

Null-Coalescing Operator

Closely related to the conditional operator is the well-sounding null-coalescing operator, which was introduced in C# 2.0 as part of the whole nullability straightening mission. When dealing with reference types or nullable value types, it sometimes makes sense to be able to supply a default value as a substitute for null. That’s precisely what the null-coalescing operator provides:

int? deposit = GetDeposit(user);AddToAccount(user, deposit ?? 0);

Written as an infix ?? operator, the null-coalescing operator first evaluates the left operand. If it results in the null reference (for a reference type) or a nullable value with no value set (HasValue is false), the right operand is evaluated to produce the result; otherwise, ...