NullPointerException.class, () -> builder.put(Maps.immutableEntry((String) null, 1)));
  }

  private static class StringHolder {
    @Nullable String string;
  }

  public void testBuilder_withMutableEntry() {
    ImmutableListMultimap.Builder<String, Integer> builder = new Builder<>();
    StringHolder holder = new StringHolder();
    holder.string = "one";
    Entry<String, Integer> entry =

        NullPointerException.class, () -> builder.put(Maps.immutableEntry((String) null, 1)));
  }

  private static class StringHolder {
    @Nullable String string;
  }

  public void testBuilder_withMutableEntry() {
    ImmutableListMultimap.Builder<String, Integer> builder = new Builder<>();
    StringHolder holder = new StringHolder();
    holder.string = "one";
    Entry<String, Integer> entry =

        NullPointerException.class, () -> builder.put(Maps.immutableEntry((String) null, 1)));
  }

  private static class StringHolder {
    @Nullable String string;
  }

  public void testBuilder_withMutableEntry() {
    ImmutableSetMultimap.Builder<String, Integer> builder = new Builder<>();
    StringHolder holder = new StringHolder();
    holder.string = "one";
    Entry<String, Integer> entry =

    assertThrows(NullPointerException.class, () -> builder.put(immutableEntry((String) null, 1)));
  }

  private static class StringHolder {
    @Nullable String string;
  }

  public void testBuilder_withMutableEntry() {
    ImmutableMap.Builder<String, Integer> builder = new Builder<>();
    StringHolder holder = new StringHolder();
    holder.string = "one";
    Entry<String, Integer> entry =