default values for implicit parameters are ignored

[smarter]

This works fine in scalac but does not compile with dotty:

class A

object Impl {
  def foo()(implicit x: A = null): Int = 2
  def test: Int = {
    foo()
  }
}

[error] try/impldef.scala:6: error: no implicit argument of type A found for parameter x of method foo in object Impl$
[error]     foo()
[error]          ^

[smarter]

Needed for tests/pending/run/Meter.scala.