.plus(Integer::class, null)
    assertThat(tags[String::class]).isEqualTo("a")
    assertThat(tags.toString()).isEqualTo("{class kotlin.String=a}")
  }

  @Test
  fun computeIfAbsentWhenEmpty() {
    val tags = EmptyTags
    val atomicTags = AtomicReference<Tags>(tags)
    assertThat(atomicTags.computeIfAbsent(String::class) { "a" }).isEqualTo("a")