code: @SuppressWarnings({"cast", "unchecked"})
      public static <K, V> EntryWeigher<K, V> entrySingleton() {
          return (EntryWeigher<K, V>) SingletonEntryWeigher.INSTANCE;
      }
docs: A weigher where an entry has a weight of <tt>1</tt>. A map bounded with
  this weigher will evict when the number of key-value pairs exceeds the
  capacity.
  
  @param <K> The key type
  @param <V> The value type
  @return A weigher where a value takes one unit of capacity.