Why does casting a null to a primitive(ie: int) in .net 2.0 throw a null ref exception and not a invalid cast exception?

Question

I was going through some code and came across a scenario where my combobox has not been initialized yet. This is in .NET 2.0 and in the following code, this.cbRegion.Select

Answer 1

If you compile

object o = null;
int a = (int)o;

and look at the MSIL code, you'll see something like

ldnull
...
unbox.any int32

Now the behavior for unbox.any is specified as follows:

InvalidCastException is thrown if obj is not a boxed type.

NullReferenceException is thrown if obj is a null reference.

This is what you see in your code.