Null handling?

[suzdalnitski]

Hi,

It seems that null values in Json can't be parsed. Eg the following fails:

`
{
    "errors": [
        {
            "extensions": {
                "code": "unauthenticated",
                "reference": null
            },
            "message": "You must be authenticated to perform this action",
            "path": [ "startPlanCheckout" ]
        }
    ]
}
`
->Js.Json.parseExn
->JsonCombinators.Json.decode(DecodeErrors.fetchResult)

My decoder is:

module DecodeErrors = {
  open JsonCombinators.Json.Decode

  type extensions = {
    code: string,
    reference: option<string>,
  }

  type error = {
    message: string,
    path: array<string>,
    extensions: extensions,
  }

  type fetchResult = {errors: option<array<error>>}

  let errorField = object(field => {
    message: field.required(. "message", string),
    path: field.required(. "path", array(string)),
    extensions: field.required(.
      "extensions",
      object(field => {
        code: field.required(. "code", string),
        reference: field.optional(. "reference", string),
      }),
    ),
  })

  let fetchResult = object(field => {
    errors: field.optional(. "errors", array(errorField)),
  })
}

This results in the following error: Expected string, got null\n\tat field 'reference'\n\ta…tensions'\n\tin array at index 0\n\tat field 'errors'

It seems that optional doesnt support nulls (which makes sense since Noneis compiled toundefined` in Rescript).

Is there a way to make nulls also be treated as optional?

Thanks!

[glennsl]

That's what option is for. Try:

reference: field.required(. "reference", option(string)),

If optional also accepted null you wouldn't be able to distinguish between the field being null and not being present at all.

[suzdalnitski]

Yup, this works for null!

However, this fails with undefined values (as expected).

Is there a way to make this work with both null and undefined? Something similar to Js.Nullable.t? I don't think I ever had a use case, where I had to distinguish between the two.

Thanks!

[glennsl]

This should work:

reference: field.optional(. "reference", option(string))->Belt.Option.flatMap(x => x),

Eventually you'll be able to use Option.flat from rescript-core.

[suzdalnitski]

That makes sense, thank you!