docs: public static Stack startIfNotEmpty() {
          Stack stack = getStack();
          if (!stack.elements.isEmpty()) {
              stack.push(CombinedInterceptorAndDecoratorStackMethodHandler.NULL_INSTANCE);
              return stack;
          } else {
              // if RequestScopedCache is not active, remove now to prevent ThreadLocal leak
              stack.removeIfEmpty();
              return null;
          }
      }