guava/src/com/google/common/collect/ImmutableMap.java
@SuppressWarnings("unchecked")
  public static <K, V> ImmutableMap<K, V> of() {
    return (ImmutableMap<K, V>) RegularImmutableMap.EMPTY;
  }
@SuppressWarnings("unchecked")
  public static <K, V> ImmutableMap<K, V> of() {
    return (ImmutableMap<K, V>) RegularImmutableMap.EMPTY;
  }
Returns the empty map. This map behaves and performs comparably to {@link
Collections#emptyMap}, and is preferable mainly for consistency and maintainability of your
code.