return "a";
  }

  @Override
  protected Collection<Integer> getValueNotInPopulatedMap() {
    return singleton(-2);
  }

  @Override
  public void testEntrySetRemoveAllNullFromEmpty() {
    try {
      super.testEntrySetRemoveAllNullFromEmpty();
    } catch (RuntimeException tolerated) {
      // GWT's TreeMap.entrySet().removeAll(null) doesn't throws NPE.
    }
  }

  @Override

    } catch (RuntimeException tolerated) {
      // GWT's HashMap.keySet().removeAll(null) doesn't throws NPE.
    }
  }

  @Override
  public void testEntrySetRemoveAllNullFromEmpty() {
    try {
      super.testEntrySetRemoveAllNullFromEmpty();
    } catch (RuntimeException tolerated) {
      // GWT's HashMap.entrySet().removeAll(null) doesn't throws NPE.
    }
  }

    } catch (RuntimeException tolerated) {
      // GWT's HashMap.keySet().removeAll(null) doesn't throws NPE.
    }
  }

  @Override
  public void testEntrySetRemoveAllNullFromEmpty() {
    try {
      super.testEntrySetRemoveAllNullFromEmpty();
    } catch (RuntimeException tolerated) {
      // GWT's HashMap.entrySet().removeAll(null) doesn't throws NPE.
    }
  }

    } else {
      assertThrows(UnsupportedOperationException.class, () -> entrySet.removeAll(entriesToRemove));
    }
    assertInvariants(map);
  }

  public void testEntrySetRemoveAllNullFromEmpty() {
    Map<K, V> map;
    try {
      map = makeEmptyMap();
    } catch (UnsupportedOperationException e) {
      return;
    }

    Set<Entry<K, V>> entrySet = map.entrySet();

    } else {
      assertThrows(UnsupportedOperationException.class, () -> entrySet.removeAll(entriesToRemove));
    }
    assertInvariants(map);
  }

  public void testEntrySetRemoveAllNullFromEmpty() {
    Map<K, V> map;
    try {
      map = makeEmptyMap();
    } catch (UnsupportedOperationException e) {
      return;
    }

    Set<Entry<K, V>> entrySet = map.entrySet();