map.put(Long.class, null);
    assertThat(map.get(Long.class)).isNull();
    assertThat(map.getInstance(Long.class)).isNull();
  }

  public void testPrimitiveAndWrapper() {
    assertThat(map.getInstance(int.class)).isNull();
    assertThat(map.getInstance(Integer.class)).isNull();

    assertThat(map.putInstance(int.class, 0)).isNull();