docs: def _mkAddBtnVisible(self):
          """
          Ensure that the Add button is visible also when there are no tabs
          """
          if not self._btn_add_height:
  #             self._btn_add_height = self.cornerWidget().height()
              self._btn_add_height = self._cwBtn.height()
          if self.count() == 0:
              
  #             self.cornerWidget().setMinimumHeight(self._btn_add_height - 8)
              self._cwBtn.setMinimumHeight(self._btn_add_height - 8)
              self.setMinimumHeight(self._btn_add_height)