To be able to expand empty rows, just enable the master view's OptionsDetail.AllowExpandEmptyDetails option. In this case, empty master rows will display a grayed out expand button, which can be clicked to expand a row. If you want this button not to be grayed out, please handle the master view's GridView.MasterRowEmpty event in the following manner:
void gridView1_MasterRowEmpty(object sender, MasterRowEmptyEventArgs e) {
e.IsEmpty = false;
}