code: private function ensureSubmitElement($panelRows)
      {
          // Check if we have a submit button.
          $hasSubmit = false;
          foreach ($panelRows as $panelRow) {
              foreach ($panelRow as $element) {
                  if ($element instanceof SubmitElementInformationInterface) {
                      $hasSubmit = true;
                      break;
                  }
  
                  if ($hasSubmit) {
                      break;
                  }
              }
          }
  
          // If not add a submit.
          if (!$hasSubmit && $panelRows->getRowCount()) {
              $row = $panelRows->getRow($panelRows->getRowCount() - 1);
              $row->addElement(new DefaultSubmitElementInformation(), 0);
          }
      }
docs: Ensure at least one submit element is present in any of the rows.
  
  If no submit element is present, this method will create one at the end of the last row.
  
  @param PanelRowCollectionInterface $panelRows The panel rows.
  
  @return void