alipay.trade.create (统一收单交易创建接口)缺少签名类型参数问题

错误如图

但我明明在下面的代码中设置成rsa了。
IAopClient client = new DefaultAopClient("https://openapi.alipaydev.com/gateway.do", app_id, merchant_private_key, "json", "RSA", alipay_public_key, charset);
AlipayTradeCreateRequest request = new AlipayTradeCreateRequest();

https://doc.open.alipay.com/docs/api.htm?docType=4&apiId=1046