如下请求参数的时候返回值为null
<xml><appid><![CDATA[xxxxx]]></appid><mch_id><![CDATA[xxxx]]></mch_id><nonce_str><![CDATA[xxxxxx]]></nonce_str><transaction_id><![CDATA[xxxx]]></transaction_id><out_refund_no><![CDATA[xxxxxxxxxxx]]></out_refund_no><total_fee><![CDATA[1]]></total_fee><refund_fee><![CDATA[1]]></refund_fee><op_user_id><![CDATA[xxxxxx]]></op_user_id><refund_desc><![CDATA[xxxxxxxxxx]></refund_desc><refund_account><![CDATA[REFUND_SOURCE_UNSETTLED_FUNDS]]></refund_account><sign><![CDATA[xxxxxxxxxxx]]></sign></xml>
你好,请检查请求url是否正确