"Optional Arguments"

// 'nickname' is optional here
public static void MethodWithOptionalArgs(string name, int age, string nickname = null) {
	// ...
}

static void Test() {
	MethodWithOptionalArgs("Ben", 30); // No nickname specified, 'null' will be passed in
}


Code snippet taken from "Two Decades of C#: A Reference - C# 2, 3 and 4".