assertThrows(NullPointerException.class, () -> multimap().putAll(source));
    expectUnchanged();
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_KEYS)
  public void testPutAllRejectsNullKey() {
    Multimap<K, V> source = getSubjectGenerator().create(mapEntry(null, v0()));
    assertThrows(NullPointerException.class, () -> multimap().putAll(source));
    expectUnchanged();
  }