code: public function setContentType($contentType)
      {
          if ($contentType instanceof ContentType) {
              $contentType = $contentType->getId();
          }
  
          $this->contentType = $contentType;
  
          $this->setType('Entry');
  
          return $this;
      }
docs: Set the content type to which results should be limited. Set to NULL to not filter for a content type.
  
  @param ContentType|string|null $contentType
  
  @return $this