I'm using this service to create a FHIR facade. 
I want to return OperationOutcome to the calling application when I detect an error. 
My code at present is :

set##class%New

If I change the response code to 422, the calling app doesn't get the OperationOutcome. Instead I get 

The custom error module does not recognize this error.
 

Do I need to implement a custom error? 

I have a quite complex FHIR Implementation Guide (IG) which is based on several other FHIR IGs. It's likely the versions of IGs conflict with each other.
From what I understand, I would need to load in all the other FHIR IG's first? 
I don't actually need FHIR profiles to be in our FHIR Repository - I'm just after terminology and the examples for our test system.
Is it possible to load a FHIR IG just as data? (I think I mean here, ignore the FHIR profiles and dependencies between them)

I'm working on FHIR project and using this code to convert an incoming request to FHIR 

Method OnRequest(request As HS.FHIRServer.Interop.Request, Output response As HS.FHIRServer.Interop.Response) As %Status

{

    #dim tSC As %Status = $$$OK

    Try {

        // Process incoming request

        set stream = ##class(HS.SDA3.QuickStream).%OpenId(request.QuickStreamId)

        set bundle = ##class(HS.FHIR.DTL.vR4.Model.Resource.Bundle).