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