*
 * <p>If your iterator supports modification through {@code remove()}, you may wish to override the
 * verify() method, which is called after each sequence and is guaranteed to be called
 * using the latest values obtained from {@link IteratorTester#newTargetIterator()}.
 *
 * <p>The value you pass to the parameter {@code steps} should be greater than the length of your

     * undergone any updates by the model builder, e.g. reflects neither inheritance nor interpolation. The model
     * identifier should be from the collection obtained by {@link #getModelIds()}. As a special case, an empty string
     * can be used as the identifier for the super POM.
     *
     * @param modelId The identifier of the desired raw model, must not be {@code null}.

     *         <code>null</code>. If it is <code>null</code>, the specified version range's recommended
     *         version is used (provided it is non-<code>null</code>). If no recommended version can be
     *         obtained, the returned version range's recommended version is set to <code>null</code>.
     *         </p>
     * @throws NullPointerException if the specified <code>VersionRange</code> is

@GwtCompatible
@ElementTypesAreNonnullByDefault
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
   * key. When a key-value pair is added to a multimap that didn't previously

     */
    @Nonnull
    Optional<Source> locate(@Nonnull Path dir);

    /**
     * Parse the model obtained previously by a previous call to {@link #locate(Path)}.
     *
     * @param source the source to parse, never {@code null}
     * @param options possible parsing options, may be {@code null}

 *
 * <p>If your iterator supports modification through {@code remove()}, you may wish to override the
 * verify() method, which is called after each sequence and is guaranteed to be called
 * using the latest values obtained from {@link IteratorTester#newTargetIterator()}.
 *
 * <p>The value you pass to the parameter {@code steps} should be greater than the length of your

   * other using {@code second = new StatsAccumulator().addAll(first).snapshot()}, if both were
   * obtained by calling {@code snapshot()} on the same {@link StatsAccumulator} without adding any
   * values in between the two calls, or if one is obtained from the other after round-tripping
   * through java serialization. However, floating point rounding errors mean that it may be false

   * valueFunction} will be applied to more than one instance of that key and, if it is, which
   * result will be mapped to that key in the returned map.
   *
   * <p>If {@code keys} is a {@link Set}, a live view can be obtained instead of a copy using {@link
   * Maps#asMap(Set, Function)}.
   *
   * @throws NullPointerException if any element of {@code keys} is {@code null}, or if {@code

 *       <b>This may change in the future.</b>
 * </ul>
 *
 * <h3>Other notes</h3>
 *
 * <ul>
 *   <li>All ranges are shallow-immutable.
 *   <li>Instances of this type are obtained using the static factory methods in this class.
 *   <li>Ranges are <i>convex</i>: whenever two values are contained, all values in between them

@GwtCompatible
@ElementTypesAreNonnullByDefault
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
   * key. When a key-value pair is added to a multimap that didn't previously