* <p>Note about generics: The signature {@code public T or(T defaultValue)} is overly
   * restrictive. However, the ideal signature, {@code public <S super T> S or(S)}, is not legal
   * Java. As a result, some sensible operations involving subtypes are compile errors:
   *
   * <pre>{@code
   * Optional<Integer> optionalInt = getSomeOptionalInt();
   * Number value = optionalInt.or(0.5); // error
   *

 * implementations, except when the table is sparse.
 *
 * <p>Null row keys or column keys are not permitted.
 *
 * <p>This class provides methods involving the underlying array structure, where the array indices
 * correspond to the position of a row or column in the lists of allowed keys and values. See the

  }

  /**
   * The supplied multimap will be mutated and an unmodifiable instance used in its stead. If the
   * multimap does not support null keys or values, alternatives may be specified for tests
   * involving nulls.
   */
  private static void checkUnmodifiableMultimap(
      Multimap<@Nullable String, @Nullable Integer> multimap,
      boolean permitsDuplicates,
      @Nullable String nullKey,

  void setBackingMap(Map<E, Count> backingMap) {
    this.backingMap = backingMap;
  }

  // Required Implementations

  /**
   * {@inheritDoc}
   *
   * <p>Invoking {@link Multiset.Entry#getCount} on an entry in the returned set always returns the
   * current count of that element in the multiset, as opposed to the count at the time the entry
   * was retrieved.
   */
  @Override