* @author Louis Wasserman
 */
@GwtCompatible
@SuppressWarnings("WrongCommentType") // false positive
abstract class AbstractMapBasedMultimap<K extends @Nullable Object, V extends @Nullable Object>
    extends AbstractMultimap<K, V> implements Serializable {
  /*
   * Here's an outline of the overall design.
   *
   * The map variable contains the collection of values associated with each