guava/src/com/google/common/collect/Multimaps.java
@Deprecated
  public static <K, V> ListMultimap<K, V> unmodifiableListMultimap(
      ImmutableListMultimap<K, V> delegate) {
    return checkNotNull(delegate);
  }
@Deprecated
  public static <K, V> ListMultimap<K, V> unmodifiableListMultimap(
      ImmutableListMultimap<K, V> delegate) {
    return checkNotNull(delegate);
  }
Simply returns its argument.

@deprecated no need to use this
@since 10.0