groupByKey() compile error after upgrading from 1.6.2 to 2.0.0

[Arun Luthra]

Here is the offending line:

val some_rdd = pair_rdd.groupByKey().flatMap { case (mk: MyKey, md_iter:
Iterable[MyData]) => {
...


[error] ******** .scala:249: overloaded method value groupByKey with
alternatives:
[error]   [K](func:
org.apache.spark.api.java.function.MapFunction[(aaa.MyKey, aaa.MyData),K],
encoder:
org.apache.spark.sql.Encoder[K])org.apache.spark.sql.KeyValueGroupedDataset[K,(aaa.MyKey,
aaa.MyData)] <and>
[error]   [K](func: ((aaa.MyKey, aaa.MyData)) => K)(implicit evidence$4:
org.apache.spark.sql.Encoder[K])org.apache.spark.sql.KeyValueGroupedDataset[K,(aaa.MyKey,
aaa.MyData)]
[error]  cannot be applied to ()
[error]     val some_rdd = pair_rdd.groupByKey().flatMap { case (mk: MyKey,
hd_iter: Iterable[MyData]) => {
[error]                                             ^
[warn] ************.scala:249: non-variable type argument aaa.MyData in
type pattern Iterable[aaa.MyData] (the underlying of Iterable[aaa.MyData])
is unchecked since it is eliminated by erasure
[warn]     val some_rdd = pair_rdd.groupByKey().flatMap { case (mk: MyKey,
hd_iter: Iterable[MyData]) => {
[warn]
                                ^
[warn] one warning found


I can't see any obvious API change... what is the problem?

Thanks,
Arun