Can I and how do I control the initial row value of a UocDropDownList RCDC control?

I am populating a DropDownListBox via a lookup of FIM objects.

My createUser rcdc has near the top the line

<my:ObjectDataSource my:TypeName="UocSearchDataSource" my:Name="search"/>

I created a reference attribute departmentRef and bound it to User type objects.

I have a custom Resource called CostCenters.

I am populating my dropdownlist control with this code:

      <my:Control my:Name="departmentRef" my:TypeName="UocDropDownList" my:Caption="Tulosyksikkö" my:Description="{Binding Source=schema, Path=departmentRef.Description}" my:RightsLevel="{Binding Source=rights, Path=departmentRef}">
        <my:Properties>
            <my:Property my:Name="Required" my:Value="True"/>
            <my:Property my:Name="Columns" my:Value="40"/>
            <my:Property my:Name="ItemSource" my:Value="{Binding Source=search, Path=CostCenters}"/>
            <my:Property my:Name="SelectedValue" my:Value="{Binding Source=object, Path=departmentRef, Mode=TwoWay}"/>
        </my:Properties>
      </my:Control>

I am very surprised to see the initial row of my List of Options being set to "<Please select an item>"

When I expand the list I see all my CostCenters beneath this "<Please select an item.>" row.

BUT, How do I get rid of this "<Please select an item>"?

I would like either a NULL initial row or the first real CostCenter.

What am I doing wrong?

Should the create rcdc not have the selectedvalue property? I am baffled where this <Please select an item> string comes from!

*HH