c# - Check if null before set to null?

Question

Should we check if variable is null before setting it to null?

if (MyBills != null) 
{
    MyBills = null;
}

For, example, in a Java related question the performance implications are minimal. Is this the case in C#? Other implications?

Testing

I've created the following code to test:

var watch = System.Diagnostics.Stopwatch.StartNew();

int iterations = int.MaxValue;
List<int> myBills= null;
for (var i = 0; i < iterations; i++)
{
    if (myBills!= null)
    {
        myBills = null;
    }
}
watch.Stop();
var elapsedMs = watch.ElapsedMilliseconds;
Console.WriteLine(elapsedMs);

Running it on rextester with and without the if (myList != null) the results are as following:

With check      Without check
988             941
938             1021
953             987
998             973
1004            1031

Average 
976.2           990.6

So, even testing it in a non-controlled environment, the performance implications are irrelevant.

Answer 1

No, there is not much use. Probably checking the variable being null or not is just as expensive as setting it to null one time too many.

If it was a property, with additional logic behind it, it could make sense to test it before, but that should actually be the responsibility of the logic in the property, not your code.