code: public function onOutput(Event $event)
      {
          if (!$event['isTarget']) {
              /*
                  All channels share the same data.
                  We only need to do this via the channel that called output
              */
              return;
          }
          $this->data = $this->debug->getData();
          $this->closeOpenGroups();
          foreach ($this->data['logSummary'] as &$log) {
              $this->removeHideIfEmptyGroups($log);
              $this->uncollapseErrors($log);
          }
          $this->removeHideIfEmptyGroups($this->data['log']);
          $this->uncollapseErrors($this->data['log']);
          $this->debug->setData($this->data);
      }
docs: debug.output subscriber
  
  @param Event $event debug.output event object
  
  @return void