FHIR Deserialize JSON FHIR to object Model

I am trying to work with the FHIR Object Model where I convert an incoming  HL7v2 to SDA then FHIR. From here I would like to be able to process the FHIR Object by deserializing it to a Bundle object using the following code my problem is I keep on getting an error  which is not explaining much about what is wrong with what I am doing any help will be appreciated  thanks.

Property FHIRAdapter As HS.JSON.AdaptorFHIR;

Method OnRequest(pRequest As HS.Message.FHIR.Request, Output pResponse As HS.Message.FHIR.Response) As %Status
{

             set pmReqFHIRobj=##class(HS.FHIR.Model.Resource.Bundle).%New()
            do ..FHIRAdapter.%FromFHIRJSON(pRequest.Payload.Read(),.pmReqFHIRobj,"HS.FHIR.Model.Resource.Bundle")

}