Stringify writes null values incorrectly

[davidbrazilparker]

I mentioned this in issue #58 But I think it is it's own issue altogether after doing some digging.

Here's an example of a data class that I serialize which has an optional serializable parameter:

@Serializable
data class Result( @Optional @SerialName("status_id") var statusId: Int? = null)

Currently with how the Kotlinx serialization library is written we write to our JSON map the value of null as a Kotlin String "null".

So for the example above the resulting JSON.stringify() return value would look as follows:

{
    "status_id":"null"
}

Cool so this will mean I'm not going to change this value when I POST this payload right? NOPE

"null" is not a valid JSON null value for the API I'm sending POST requests to. Now I'll admit I don't have much experience with API's (I'm learning 🤓). But for my use case in particular this a huge issue. Now for what I think could be the solution.

In the following file:
https://github.com/Kotlin/kotlinx.serialization/blob/master/runtime/common/src/main/kotlin/kotlinx/serialization/json/JsonParser.kt#L23

Change this line:

internal const val NULL = "null"

to

internal const val NULL = null

[qwwdfsad]

@Serializable
data class Clz(@Optional @SerialName("status_id") var statusId: Int? = null)

@Test
fun foo() {
  val r = Clz()
  println(Json.plain.stringify(Clz.serializer(), r))
}

Will print {"status_id":null} in current dev branch.
Could you please provide a self-contained example?

[davidbrazilparker]

Ah must be my current version. I'll look into this and see if I can resolve it by updating. Thanks for looking into this.