Why does Spark require SCALA_HOME?

[RJ Nowling]

Hi all,

I noticed that building the Spark RPMs required SCALA_HOME to be set.

I'm confused about this since building Spark from source doesn't require
SCALA_HOME -- Scala libraries are automatically downloaded and packaged by
maven.

Does BigTop create a separate Scala package?  Or does Debian provide a
Scala package?

Thanks!
RJ