* @since 2.0
 */
@GwtCompatible
public abstract class ComparisonChain {
  private ComparisonChain() {}

  /** Begins a new chained comparison statement. See example in the class documentation. */
  public static ComparisonChain start() {
    return ACTIVE;
  }

  private static final ComparisonChain ACTIVE =
      new ComparisonChain() {
        @SuppressWarnings("unchecked") // unsafe; see discussion on supertype

                    return new Ordering<Entry<String, String>>() {
                      @Override
                      public int compare(Entry<String, String> left, Entry<String, String> right) {
                        return ComparisonChain.start()
                            .compare(left.getKey(), right.getKey(), Ordering.natural().nullsFirst())
                            .compare(