Unbinding in game settings

I want to make bind settings, and I have problem with unbinding
I have two binds, main and alternative, and I want to remove bind when backspace is pressed
But ChangeBinding(index).Erase(); is removing it, not setting to null or <no bind>
How can I replace bind with null/<no bind>?

Forward [W] [↑] > when pressed backspace on alternative > [W] [ ]

Back ~~[↓]~~
Left [A] [←]
Right [D] [→]

Ok, found the answer:
bindAction.ApplyBindingOverride(id, "");
“” works as null