code: void clear()
      {
          NodeBuilder current = this;
          while (current != null && current.upperBound != null)
          {
              current.clearSelf();
              current = current.child;
          }
          current = parent;
          while (current != null && current.upperBound != null)
          {
              current.clearSelf();
              current = current.parent;
          }
      }
docs: ensure we aren't referencing any garbage