Encoder should remove None: Option[T] values

[mikaelstaldal]

It would be nice if the Encoder would remove the key/value completely when the type is Option[T] and the value is None. Currently, it encodes None to JSON null.

(Json4s works this way.)

This code:

  case class Test(foo: String, bar: Option[String])
  implicit val testEncoder: Encoder[Test] = deriveEncoder
  println(Test("FOO", None).asJson.noSpaces)

currently prints:

{"foo":"FOO","bar":null}

I would like it to be:

{"foo":"FOO"}

[vpavkin]

@mikaelstaldal you should just use a custom Printer with dropNullKeys = true.
By default it's false.

[mikaelstaldal]

Ah, that works. But it seems like dropNullKeys by default is false?

This is also something that is missing from documentation.

[vpavkin]

yes, it's false :) I made a mistake and fixed the comment afterwards

[ckozak]

What was the reason to make dropNullKeys = false by default? It seems that not putting nulls is more common among other libraries.

[bergmark]

I commented on this elsewhere, so a quick repeat:

My take is that the printer should not modify the actual JSON format. This is something each Encoder should decide for itself. Inevitably there will be a case where you want to combine the two options for different types, AFAICT that's not possible at the moment.

[Mahoney]

Could nested options be interpreted differently? For
case class Foo(bar: Option[Option[String]])
Foo(bar = None) = {}
Foo(bar = Some(None)) = {"bar": null}
Foo(bar = Some(Some("actual data"))) = {"bar": "actual data"}

[naderghanbari]

I agree that Printer should not touch the JSON by default. I also agree that Printer should have the power to make the result nicer if you want to. This could help in cases where the actual value is null (e.g. Java interop). So I think Printer is just fine as is.

I think the encoder, though, should drop None values by default and not encode them as null. It should, however, encode genuine null values as null and not drop them.

Similar to dropNullKeys = false in Printer, I think the encoder configuration can have something like dropNone = true.

[travisbrown]

Now that we have dropNullValues on both the printer and Json I think we can close this.