当我执行下面的代码时给予错误“java.lang.IllegalArgumentException：要求失败：未注册任何输出操作，因此没有要执行的内容”任何人都可以帮助我吗？

val ssc = new StreamingContext(sc, Seconds(1))

    val sqlContext = new org.apache.spark.sql.SQLContext(sc)

   var imput: SimpleDateFormat   = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss",  Locale.ENGLISH)
   var dia: SimpleDateFormat   = new SimpleDateFormat("dd")
   var mes: java.text.SimpleDateFormat = new SimpleDateFormat("MM");
   var ano: java.text.SimpleDateFormat = new SimpleDateFormat("yyyy");

var diacv: String = ""
var mescv: String = ""
var anocv: String = ""

case class Data(diacv: String, mescv: String, anocv: String)

val columns = Seq("timecol")

val data = ssc.cassandraTable("smartgrids","analyzer_temp")
              .select(columns.map(ColumnName(_)).take(1):_*)

val dstream = new ConstantInputDStream(ssc, data)

class foo() {

import sqlContext.implicits._

        val result = dstream.map(row => (
                     diacv = dia.format(imput.parse(row.toString())), 
                     mescv = mes.format(imput.parse(row.toString())), 
                     anocv = ano.format(imput.parse(row.toString()))
                   )           
       ).toDF()

             result.registerTempTable("result") 

            // return result
}

ssc.start()
ssc.awaitTermination()