nullSingleton = new Target(Collections.singleton(null), "nullSingleton");
  }

  // retainAll(empty)

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(ZERO)
  public void testRetainAll_emptyPreviouslyEmpty() {
    expectReturnsFalse(empty);
    expectUnchanged();
  }

  @CollectionFeature.Require(absent = SUPPORTS_REMOVE)
  @CollectionSize.Require(ZERO)