Functions in ExplodeFunctionUtil should handle null data to avoid NPE

    val t = tEnv.fromValues(
      DataTypes.ROW(
        DataTypes.FIELD("a", DataTypes.INT()),
        DataTypes.FIELD("b", DataTypes.ARRAY(DataTypes.STRING()))
      ),
      row(1, Array("aa", "bb", "cc")),
      row(2, null),
      row(3, Array("dd"))
    )
    tEnv.registerTable("T", t)

    tEnv.executeSql("SELECT a, s FROM T, UNNEST(T.b) as A (s)").print()

Caused by: java.lang.NullPointerException
	at scala.collection.mutable.ArrayOps$ofRef$.length$extension(ArrayOps.scala:192)
	at scala.collection.mutable.ArrayOps$ofRef.length(ArrayOps.scala:192)
	at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:32)
	at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:186)
	at org.apache.flink.table.planner.plan.utils.ObjectExplodeTableFunc.eval(ExplodeFunctionUtil.scala:34)