[WPF] ComboBox and ItemSource: add one empty row

Hi,

I have a ComboBox, defined as:

DataContext="{StaticResource DomainDataViewModel}"

ItemsSource="{Binding SchedTypes}"

DisplayMemberPath="Description"

Width="120">

I would insert, in head, an empty item or empty called "Select all".

So:

1) I defined a StaticResource:

2) Edit my Combobox as:

DataContext="{StaticResource DomainDataViewModel}"

DisplayMemberPath="Description"

Width="120">

The problem: in the ComboBox I see only "Select all" and not other item from my Collection and when I select "Select all", it does not stay selected.

Thanks.