code: @Override public ImmutableSet<Entry<K, V>> entries() {
      ImmutableSet<Entry<K, V>> result = entries;
      return (result == null)
          ? (entries = new EntrySet<K, V>(this))
          : result;
    }
docs: Returns an immutable collection of all key-value pairs in the multimap.
  Its iterator traverses the values for the first key, the values for the
  second key, and so on.