guava/src/com/google/common/collect/ImmutableListMultimap.java
public static <K, V> ImmutableListMultimap<K, V> of(K k1, V v1) {
    ImmutableListMultimap.Builder<K, V> builder = ImmutableListMultimap.builder();
    builder.put(k1, v1);
    return builder.build();
  }
public static <K, V> ImmutableListMultimap<K, V> of(K k1, V v1) {
    ImmutableListMultimap.Builder<K, V> builder = ImmutableListMultimap.builder();
    builder.put(k1, v1);
    return builder.build();
  }
Returns an immutable multimap containing a single entry.