Demonstrates a regression bug introduced by Scala 2.12.7 update

Scala_2_12_7_regression.scala

import org.scalatest.Matchers._

object SampleApp extends scala.App {

  implicit class IterableOps[A](private val self: Iterable[A]) extends AnyVal {
    def countUniqueItems: Map[A, Int] = ??? // implementation doesn't matter
  }

  // Fails to compile on Scala 2.12.7 and 2.12.8 with the following error:
  // [error] <CUT>/scalatest-issue/src/main/scala/SampleApp.scala:13:24: could not find implicit value for parameter emptiness: org.scalatest.enablers.Emptiness[Map[A,Int]]
  // [error]   Nil.countUniqueItems shouldBe empty
  // [error]                        ^
  Nil.countUniqueItems should have size 0

  // Compiles successfully
  (Nil.countUniqueItems: Map[Nothing, Int]) shouldBe empty

  //new IterableOps(Nil).countUniqueItems shouldBe empty

  // Compiles as well
  val ops = new IterableOps(Nil)
  ops.countUniqueItems shouldBe empty
}