.addUnsafeNonAscii("header1", "valué1")
        .build()
    assertThat(headers.toString()).isEqualTo("header1: valué1\n")
  }

  // Fails on JS, ClassCastException: Illegal cast
  @Test fun ofMapThrowsOnNull() {
    assertFailsWith<NullPointerException> {
      (mapOf("User-Agent" to null) as Map<String, String>).toHeaders()
    }
  }

  @Test fun toMultimapGroupsHeaders() {
    val headers =