Flink报错：org.apache.flink.api.common.InvalidProgramException:

val datas  = env.fromElements((1, "aa", 9), (3, "bb", 7) , (2, "bb", 6),
        (2, "aa", 6), (2, "aa", 6), (2, "aa", "6"))
    datas.distinct().print()

Picked up _JAVA_OPTIONS: 
Exception in thread "main" org.apache.flink.api.common.InvalidProgramException: This type (GenericType) cannot be used as key.
	at org.apache.flink.api.common.operators.Keys$ExpressionKeys.(Keys.java:327)
	at org.apache.flink.api.common.operators.Keys$ExpressionKeys.(Keys.java:291)
	at org.apache.flink.api.common.operators.Keys$ExpressionKeys.(Keys.java:222)
	at org.apache.flink.api.java.operators.DistinctOperator.(DistinctOperator.java:59)
	at org.apache.flink.api.scala.DataSet.distinct(DataSet.scala:990)
	at com.sydney.dream.flinkdemo.FlinkDatasetApi$.distinct(FlinkDatasetApi.scala:50)
	at com.sydney.dream.flinkdemo.FlinkDatasetApi$.main(FlinkDatasetApi.scala:43)
	at com.sydney.dream.flinkdemo.FlinkDatasetApi.main(FlinkDatasetApi.scala)

给的数据中，tuple的第三个元素的值，是object类型（有数字6，也有字符串“6”），不可以当做key。
正确如下：

 val datas  = env.fromElements((1, "aa", 9), (3, "bb", 7) , (2, "bb", 6),
           (2, "aa", 6), (2, "aa", 6), (2, "aa", 6))
       datas.distinct().print()