docs: @CheckForNull
      @SuppressWarnings( "NP_BOOLEAN_RETURN_NULL" )
      public Boolean setNodeAvailable( final K key, final boolean available ) {
          final ManagedItem<Boolean> item = _map.get( key );
          final Boolean availableObj = Boolean.valueOf( available );
          if ( item == null || item._value != availableObj ) {
              final ManagedItem<Boolean> previous =
                      _map.put( key, new ManagedItem<Boolean>( availableObj, System.currentTimeMillis() ) );
              return previous != null
                  ? previous._value
                  : null;
          } else {
              return item._value;
          }
      }