How do I detect if no selected item on ComboBox is chosen?

Question

In my ComboBox, the field is blank before users click it and choose any item. So without users click on the ComboBox, it remains empty. How do we check whether the ComboBox is empty or not?

This codes gives me an error because there is no item selected yet:

if( ComboBox.SelectedItem.ToString().Equals("") )
{
     //do something
}

Answer 1

if( ComboBox.SelectedItem == null ) {
   // do something
}