code: protected function getFormActionFromRequest(HTTPRequest $r)
      {
          $action = $r->requestVar('action');
          $formAction = $this->record->findActionByName($action);
  
          if (!$formAction instanceof BetterButtonNestedForm) {
              throw new Exception("Action $action doesn't exist or is not a BetterButtonNestedForm");
          }
  
          return $formAction;
      }
docs: Get the action from the request, whether it's part of the form data
  or in the query string
  
  @param  HTTPRequest $r
  @return BetterButtonNestedForm
  @throws Exception If the action doesn't exist, or isn't a BetterButtonNestedForm