guava/src/com/google/common/collect/AbstractSortedSetMultimap.java
@Override
  public SortedSet<V> get(@Nullable K key) {
    return (SortedSet<V>) super.get(key);
  }
@Override
  public SortedSet<V> get(@Nullable K key) {
    return (SortedSet<V>) super.get(key);
  }
Returns a collection view of all values associated with a key. If no mappings in the multimap
have the provided key, an empty collection is returned.

<p>Changes to the returned collection will update the underlying multimap, and vice versa.

<p>Because a {@code SortedSetMultimap} has unique sorted values for a given key, this method
returns a {@link SortedSet}, instead of the {@link Collection} specified in the {@link
Multimap} interface.