Using a closure object marshaller which returns null results in out of sequence exceptions.

[chriserickson]

I'd like to handle optionals via marshalling:

    JSON.registerObjectMarshaller(Optional) { Optional optional ->
         if (optional.present)
             return optional.get()
         else
             return null
    }

    assert (["Test": Optional.empty()] as JSON).toString(false) == '{"Test":null}' // throws out of sequence exception.

It appears to fail because the ClosureObjectMarshaller doesn't write a null value when the closure returns a null.

[ccarcaci]

The same for me :(

[gantaa]

After upgrading to Grails 3, I am unable to get any JSON with null attributes to marshal successfully. I used to use the JSONObject.NULL, which would marshal into null on the client, but has since been removed. My stuff now fails cuz ClosureObjectMarshaller cant handle the null... apache/grails-core#9129 I tried JSONNull, that marshals as the fully qualified class name as a String. Not sure what the correct way to do this is. JSON views? I'd prefer my nulls to be null, not empty strings or false