private static <T> @Nullable Class<? extends T> getImplementation(Class<T> type) {
    return (Class<? extends T>) implementations.get(type);
  }

  private static final Logger logger = Logger.getLogger(ArbitraryInstances.class.getName());

  /**
   * Returns an arbitrary instance for {@code type}, or {@code null} if no arbitrary instance can be
   * determined.
   */

  private static <T> @Nullable Class<? extends T> getImplementation(Class<T> type) {
    return (Class<? extends T>) implementations.get(type);
  }

  private static final Logger logger = Logger.getLogger(ArbitraryInstances.class.getName());

  /**
   * Returns an arbitrary instance for {@code type}, or {@code null} if no arbitrary instance can be
   * determined.
   */