For everyone's reference, this could only be a bug. The way you know that is the error message:
<console>:13: error: type mismatch;
found : List[Int]
required: List[A]
List[A] is not a real type - it is List applied to its own type parameter. That is not a type which can be required since it is not a type which can be expressed.
[Edit - it's too early, who knows what I'm talking about. Ignore the above, but you can still follow the link.]
The relevant ticket for this is https://issues.scala-lang.org/browse/SI-6472 .