code: public function handle(EncodePropertyValueFromWidgetEvent $event)
      {
          if (('tl_metamodel_dca_combine' !== $event->getEnvironment()->getDataDefinition()->getName())
              || ('rows' !== $event->getProperty())) {
              return;
          }
  
          $environment  = $event->getEnvironment();
          $dataProvider = $environment->getDataProvider();
          $properties   = $environment->getDataDefinition()->getPropertiesDefinition();
  
          $values = (array) $event->getValue();
          foreach ($values as $row => $current) {
              $values[$row] = $this->updateValues($current, $properties, $dataProvider);
          }
  
          $event->setValue($values);
      }
docs: Handle event to update the empty type safety values for DCA combinations.
  
  @param EncodePropertyValueFromWidgetEvent $event The event.
  
  @return void