为什么在.net 2.0中向原语（即：int）转换null会抛出空引用异常而不是无效的强制转换异常？

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.SelectedValue is null.I was going through some code and came across a