code: public void setTextForNullSelection(String text) {
  
          // do nothing if there's no null option
          CmsLabelSelectCell cell = m_selectCells.get("");
          if (cell == null) {
              return;
          }
          cell.setText(text);
          // if the null option is selected, we still need to update the opener
          if (CmsStringUtil.isEmptyOrWhitespaceOnly(m_selectedValue)) {
              selectValue("");
          }
      }
docs: Sets the text that is used for the "not selected" option.<p>
  
  @param text the text which should be used for the "not selected" option