try {
      builder.putAll(Collections.<String, Integer>singletonMap("one", null));
      fail();
    } catch (NullPointerException expected) {
    }
  }

  @SuppressWarnings("AlwaysThrows")
  public void testPuttingTheSameKeyTwiceThrowsOnBuild() {
    Builder<String, Integer> builder =
        new Builder<String, Integer>()
            .put("one", 1)

    try {
      builder.putAll(Collections.<String, Integer>singletonMap("one", null));
      fail();
    } catch (NullPointerException expected) {
    }
  }

  @SuppressWarnings("AlwaysThrows")
  public void testPuttingTheSameKeyTwiceThrowsOnBuild() {
    Builder<String, Integer> builder =
        new Builder<String, Integer>()
            .put("one", 1)