docs: public static <K, V> Map<K, V> copyAsMap(Multimap<K, V> multimap) {
      final Map<K, Collection<V>> inputAsMap = multimap.asMap();
      final ImmutableMap.Builder<K, V> ret = ImmutableMap.builder();
  
      for (final Map.Entry<K, Collection<V>> mapping : inputAsMap.entrySet()) {
        ret.put(mapping.getKey(), Iterables.getOnlyElement(mapping.getValue()));
      }
  
      return ret.build();
    }