Question

Surprisingly the code bellow will not succeed.

int? n1 = null; int? n2 = null; Assert.IsTrue(n1 <= n2);  // Fails here 

Do you know why?

Answer 1

Using boolean logic with null nullable values in C# (and VB.Net) often times defies logic. I find the best way to make sense of it is to remember that ‘null is not a value’. Because null is not a value you cannot do any operations on it. Hence things like ‘1 > null‘ and ‘1 < null‘ are both true.

Here is a detailed guide: http://msdn.microsoft.com/en-us/library/2cf62fcy.aspx

If you do want to treat null as a value then you could use the GetValueOrDefaultMethod() to equate null with the default value. For example

Assert.IsTrue(n1.GetValueOrDefault() <= n2.GetValueOrDefault());  // True 

This is a bit verbose but it will get the job done.