We all know that defining a nullable type in C# is very simple as below

int? value;

And when you want to check whether the value is null, then there are definitely multiple way you could do.

// First option.
if(value == null)
{
    //Write the code here
}

// Second Option.
if(!value.HasValue)
{
   //Write the code here
}

However there is a easy way you could specify the default value i.e., the default value to be used in case the nullable type has a null value in it.

// The below will set the index to 10 if value is null.
int index = value ?? 10;

// This will check for both value1 and value2 for null and then assigns the value as null.
int index = value1 ?? value2 ?? 10;
Tip: Null Coalescing Operator To Define Default Value For Nullable Types – Double Question Mark