NPE from SHOW PARTITIONS for null partition values

  test("null and empty string as partition values") {
    import testImplicits._
    withNamespaceAndTable("ns", "tbl") { t =>
      val df = Seq((0, ""), (1, null)).toDF("a", "part")
      df.write
        .partitionBy("part")
        .format("parquet")
        .mode(SaveMode.Overwrite)
        .saveAsTable(t)

      runShowPartitionsSql(s"SHOW PARTITIONS $t", Row("part=null") :: Nil)
    }
  }

java.lang.NullPointerException was thrown.
java.lang.NullPointerException
	at org.apache.spark.sql.execution.datasources.v2.ShowPartitionsExec.$anonfun$run$3(ShowPartitionsExec.scala:58)
	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:238)