constrparams.scala:4: type mismatch;
 found   : scala.AllRef
 required: x.t
  private val z: x.t = null; //error
                       ^
constrparams.scala:1: type x.type escapes its defining scope as part of scala.Object { type t,  val y$: x.type,  def y: x.type,  val z$: x.t,  def z: x.t }
abstract class C(x: C) {
               ^
two errors found