public void testNotEqualsEmpty() {
    new EqualsTester()
        .addEqualityGroup(getMultiset())
        .addEqualityGroup(getSubjectGenerator().create())
        .testEquals();
  }

  public void testHashCodeMatchesEntrySet() {
    assertEquals(getMultiset().entrySet().hashCode(), getMultiset().hashCode());
  }

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