当我使用大猩猩/ RPC / JSON时如何为参数设置空值？

I tried to send a request to a RPC interface, but the interface doesn't need params. It means the params field should be "params":[], but when I use json.EncodeClientRequest(method string, args interface{}), the value of params is always "params":[{}] or "params":[null]. So it always causes the error: map[code:-32602 message:Invalid method parameters]. How could I set a null value for params. Next is my request struct:

// request struct
type JsonRpcReq struct {
    Id      uint32       `json:"id"`
    Url     string       `json:"url"`
    Method  string       `json:"method"`
    Params  *interface{} `json:"params"`
    JsonRpc string       `json:"jsonrpc"`
}

The error of sentence is:

// request method
func (r *JsonRpcReq) Send() (interface{}, error) {
    message, err := json.EncodeClientRequest(r.Method, r.Params)
    fmt.Println(string(message))
    if err != nil {
        return nil, err
    }
    ...
}

The request sentence is:

req := NewJsonRpcReq("http://finance.test.cppp.com/rpc/healthCheck", "status", nil)

The NewJsonRpcReq method is:

func NewJsonRpcReq(url, method string, params *interface{}) *JsonRpcReq {
    return &JsonRpcReq{Id: 0, Url: url, Method: method, Params: params, JsonRpc: "2.0"}
}