code: @SuppressWarnings("unchecked")
      public static final <K,V> SortedMap<K,V> emptySortedMap() {
          return (SortedMap<K,V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP;
      }
docs: Returns an empty sorted map (immutable).  This map is serializable.
  
  <p>This example illustrates the type-safe way to obtain an empty map:
  <pre> {@code
  SortedMap<String, Date> s = Collections.emptySortedMap();
  }</pre>
  
  @implNote Implementations of this method need not create a separate
  {@code SortedMap} object for each call.
  
  @param <K> the class of the map keys
  @param <V> the class of the map values
  @return an empty sorted map
  @since 1.8