Func<string, string> concatName = (name) =>
{
    name = name ?? "Anurag";
    return "Welcome " + name;
};

Console.WriteLine(concatName(null));
Console.WriteLine(concatName("Rahul"));

/*After.....*/
Console.WriteLine("--------------DEFAULT LAMBDA PARAMETERS---------------------------");

var concatNameNew = (string name = "Anurag") =>
{
    return "Welcome " + name;
};
Console.WriteLine(concatNameNew());
Console.WriteLine(concatNameNew("Rahul"));