code: protected function resolveItemAction(AbstractDiffItem $item)
      {
          if ($item instanceof CreateDiffItem) {
              $action = ActionTypes::CREATE;
  
              return $action;
          } elseif ($item instanceof DeleteDiffItem) {
              $action = ActionTypes::DELETE;
  
              return $action;
          } elseif ($item instanceof UpdateDiffItem) {
              $action = ActionTypes::UPDATE;
  
              return $action;
          } else {
              throw new \InvalidArgumentException('Unsupported diff item type. Got: ' . get_class($item));
          }
      }
docs: Returns action letter depending on item class.
  
  @param AbstractDiffItem $item
  
  @return string
  @throws \InvalidArgumentException