panic when param of map mismatch

[chowyu12]

go-zero v1.4.2

error:
panic: reflect.Value.SetMapIndex: value of type interface {} is not assignable to type string

test code:

        type Req struct {
		Params map[string]string `json:"params"` // 参数
	}

	var req Req
	body := `{"params":{"a":{"a":123}}}`
	err := mapping.UnmarshalJsonReader(strings.NewReader(body), &req)
	if err != nil {
		fmt.Println(err)
		return
	}

[chowyu12]

@anqiansong @kevwan

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@anxi sends @Kev to play