@Override
 public Set<RoleProxy> getValue() {
   return roleCheckboxCell.getRolesSet();
 }
 public void setReadonly(boolean readonly) {
   roleCheckboxCell.setReadonly(readonly);
 }
 @Override
 public void setValue(Set<RoleProxy> value) {
   roleCheckboxCell.setRolesSet(value);
   this.redraw();
 }