how insert 'empty' domain combobox organization datatable

i have combo box winforms app an vigilant competence selected, nonetheless mandatory. i therefore need an 'empty' initial vigilant infer value set.

the combo box organization datatable being returned stored way (i offer apologies hungarian footnote ui controls :p ):

 datatable hierarchies = _database.getavailablehierarchies(cmbdatadefinition.selectedvalue.tostring()).copy();//calls sp
 cmbhierarchies.datasource = hierarchies;
 cmbhierarchies.valuemember = "guid";
 cmbhierarchies.displaymember = "objectlogicalname";

how i insert such an lifeless item?

i have opening change sp, nonetheless i unequivocally move 'pollute' ui logic.

update: datatable.newrow() i blanked on, thanks. i have upmodded (all 3 answers distant anyway). i am perplexing iterator settlement operative before i endorse an 'answer'

update: i cruise correct puts me village wiki land, i have solid mention unparalleled answer, have effect context domains. interjection your common input.