scala2.12で呼び出し元でstream closedになるケース

readGZIP.scala

  def readGZIPFile[A](filePath: String, proc: String => Option[A]): Either[Throwable, Seq[A]] = {
    val gs = new GZIPInputStream(new FileInputStream(filePath))
    val ss = Source.fromInputStream(gs, "UTF-8")
    try {
      val ret = ss.getLines().flatMap(line => proc(line)).toSeq
      Right(ret)
    } catch {
      case NonFatal(t) => Left(t)
    } finally {
      ss.close()
    }
  }