Scalaで例外を定義 ref: http://qiita.com/mather314/items/b36a8f2832f0851d3eb7

file0.scala

class MyException(message: String = null, cause: Throwable = null) extends RuntimeException(message, cause) {
  def this(cause: Throwable) = this(Option(cause).map(_.toString).getOrElse(null), cause)
}

file1.scala

new MyException()
new MyException("msg")
new MyException(new Exception("hoge"))
new MyException("addtional message", new Exception("hoge"))

file2.scala

new MyException(cause = new Exception("hoge"))