android/guava/src/com/google/common/collect/ImmutableSortedMap.java
@SuppressWarnings("unchecked")
  // unsafe, comparator() returns a comparator on the specified type
  // TODO(kevinb): evaluate whether or not of().comparator() should return null
  public static <K, V> ImmutableSortedMap<K, V> of() {
    return (ImmutableSortedMap<K, V>) NATURAL_EMPTY_MAP;
  }
@SuppressWarnings("unchecked")
  // unsafe, comparator() returns a comparator on the specified type
  // TODO(kevinb): evaluate whether or not of().comparator() should return null
  public static <K, V> ImmutableSortedMap<K, V> of() {
    return (ImmutableSortedMap<K, V>) NATURAL_EMPTY_MAP;
  }
Returns the empty sorted map.