kafka-streams project compiles using maven but failed using sbt

[Tommy Go]

Hi

I am playing with kafka-streams using Scala, but found some strange issue,
the following project compiles using mvn but failed using sbt:

https://github.com/deeplambda/kstream-debug

[error] 
/Users/tommy/tmp/kstream-debug/src/main/scala/kafka/streams/WordCountDemo.scala:49:
missing parameter type for expanded function ((x$1) =>
x$1.toUpperCase())
[error]     val uppercasedWithMapValues: KStream[Array[Byte], String]
= textLines.mapValues(_.toUpperCase())
[error]
                     ^
[error] one error found
[error] (compile:compileIncremental) Compilation failed



Any ideas why the demo failed compiling using sbt ?

Thanks,
Tommy