final transient K singleKey;
  final transient V singleValue;

  SingletonImmutableBiMap(K singleKey, V singleValue) {
    checkEntryNotNull(singleKey, singleValue);
    this.singleKey = singleKey;
    this.singleValue = singleValue;
    this.inverse = null;
  }

  private SingletonImmutableBiMap(K singleKey, V singleValue, ImmutableBiMap<V, K> inverse) {
    this.singleKey = singleKey;

  }

  @Override
  public int size() {
    return 1;
  }

  @Override
  ImmutableSet<Cell<R, C, V>> createCellSet() {
    return ImmutableSet.of(cellOf(singleRowKey, singleColumnKey, singleValue));
  }

  @Override
  ImmutableCollection<V> createValues() {
    return ImmutableSet.of(singleValue);
  }

  @Override
  @J2ktIncompatible
  @GwtIncompatible

  private final K singleKey;
  private final V singleValue;

  @Nullable transient SingletonImmutableBiMap<V, K> inverse;

  SingletonImmutableBiMap(K key, V value) {
    super(singletonMap(checkNotNull(key), checkNotNull(value)));
    this.singleKey = key;
    this.singleValue = value;
  }

  private SingletonImmutableBiMap(K key, V value, SingletonImmutableBiMap<V, K> inverse) {

                final Set<String> sortFieldNames = new HashSet<>();
                for (final String defaultSortValue : defaultSortValues) {
                    for (final String singleValue : defaultSortValue.split(",")) {
                        final String sortFieldName = singleValue.split("\\.")[0];
                        if (!sortFieldNames.contains(sortFieldName)) {
                            sortFieldNames.add(sortFieldName);