Gin [ProtoBuf Render] why not use Data proto.Message directly

just a question render/protobuf.go

type ProtoBuf struct {
    Data any
}

var protobufContentType = []string{"application/x-protobuf"}

// Render (ProtoBuf) marshals the given interface object and writes data with custom ContentType.
func (r ProtoBuf) Render(w http.ResponseWriter) error {
    r.WriteContentType(w)

    bytes, err := proto.Marshal(r.Data.(proto.Message))

why not use proto.Message for Data directly?

type ProtoBuf struct {
    Data proto.Message
}
.....
    bytes, err := proto.Marshal(r.Data)