Compiler version
3.1.1
Minimized code & Output
scala> case class Foo(x: Int)(xs: String*)
// defined case class Foo
scala> Foo(3)
-- [E081] Type Error: ----------------------------------------------------------
1 |Foo(3)
  |^
  |Missing parameter type
  |
  |I could not infer the type of the parameter xs.
1 error found
Expectation
Notify the user that the argument list for xs is mandatory instead of telling them that the type cannot be inferred.