Check if any variable conforms any interface using generics in Go - go

Question

I am writing an API using go-fiber, and I want to check, if passed JSON conforms an interface that I want to see. So I decided to use 1.18's feature - generics. Here is what I did, but it does not work due to type problem.
func checkDataConformsInterface[I any](format I, c *fiber.Ctx) (I, error) {
if err := c.BodyParser(&format); err != nil {
return nil, err
}
return c.JSON(format), nil
}
The errors say
src/endpoints/v1/tasks.go:36:10: cannot use nil as I value in return statement
src/endpoints/v1/tasks.go:39:9: cannot use c.JSON(format) (value of type error) as type I in return statement
And I want to call the function like this:
type CreateTaskDF struct {
Target string `json:"target"`
Deepness int `json:"deepness"`
}
func CreateTask(c *fiber.Ctx) error {
data, err := checkDataConformsInterface[CreateTaskDF](&CreateTaskDF{}, c)
if err != nil {
log.Fatal(err)
}
// work with data here
...
How should I convert the return value in the function to make it work? Thanks!

Answer 1

It probably could work like this(if you do not consider any lib-based payload validators, which exist in almost every golang routing lib or web framework). So, to just validate your data you can use this:
func checkDataConformsInterface[I any](format I, c *fiber.Ctx) bool {
if err := c.BodyParser(&format); err != nil {
return false
}
return true
}

Answer 2

So I came up with the following solution
func checkDataConformsInterface[I any](format *I, c *fiber.Ctx) error {
if err := c.BodyParser(&format); err != nil {
return err
}
err := c.JSON(format)
if err != nil {
return err
}
return nil
}
which can be called like
func CreateTask(c *fiber.Ctx) error {
parsedData := CreateTaskDF{}
err := checkDataConformsInterface[CreateTaskDF](&parsedData, c)
if err != nil {
c.SendStatus(400)
return c.SendString("Wrong data")
}
Please, point me the problems if any