code: public static <K> Matcher<Multimap<K, ?>> hasSameKeySet(final Multimap<K, ?> comparison) {
          return IsMultimapWithKeySet.hasSameKeySet(comparison.keySet());
      }
docs: Creates a matcher for {@linkplain Multimap} matching when the examined object has exactly the same key set of the
  given comparison {@code Multimap}.