public function getReturnTypes() {
    $types = ['void'];
    $doc_comment = $this->getDocComment();
    if (!$doc_comment) {
      return $types;
    }
    $return_tag = $doc_comment->getReturn();
    if (!$return_tag) {
      return $types;
    }
    $types = Types::normalize($return_tag->getTypes());
    if (empty($types)) {
      $types[] = 'void';
    }
    return $types;
  }