test("SPARK-XXXXX: empty partition values are written as null partitions") {
  withTempDir { dir =>
    val path = dir.getCanonicalPath

    Seq(
      (1, ""),
      (2, "a"),
      (3, null.asInstanceOf[String])
    ).toDF("id", "part")
      .write
      .partitionBy("part")
      .parquet(path)

    val fs = new Path(path).getFileSystem(spark.sessionState.newHadoopConf())
    val partitions = fs.listStatus(new Path(path))
      .filter(_.isDirectory)
      .map(_.getPath.getName)
      .sorted

    assert(partitions.contains("part=a"))

    // Empty string should not generate a dedicated partition directory.
    assert(!partitions.contains("part="))

    // Empty string and null should both map to the default partition.
    assert(partitions.count(_.startsWith("part=__HIVE_DEFAULT_PARTITION__")) == 1)

    checkAnswer(
      spark.read.parquet(path).groupBy("part").count(),
      Row(null, 2) :: Row("a", 1) :: Nil
    )
  }
}