code: public function union($set, ...$sets): array
      {
          array_unshift($sets, $set);
          array_unshift($sets, $this);
          $keys = [];
          foreach ($sets as $key) {
              $keys[] = ($key instanceof self) ? $key->key : $key;
          }
  
          return $this->unSerializeArray($this->redis->sunion($keys));
      }
docs: @param string|self $set First set or key.
  @param array<int, string|self> $sets,... More sets or keys. Can be mixed.
  
  @return mixed[] List of members of resulting set.