Web flow in Grails - confused

I have nothing but pain every time I touch web flow, I thought things might be more simple and understanable in the world of grails as apposed to Spring MVC but it seems not.

I have a simple situation where I want to start off a web flow with a prepopulated command object already in the flow scope when the first page of the web flow displays. The command object is basically going to hold copies of values form a domain object

heres my command object:

@grails.validation.Validateable(nullable=false)
class PatientEditFlowCommand implements Serializable{

StepOneCommand stepOneCommand

PatientEditFlowCommand(Patient patient){

    stepOneCommand = new StepOneCommand(
            patientName : "${patient.appUser?.firstName} ${patient.appUser?.lastName}",
            patientDoctorId : patient.doctor?.id,
            patientNurseId : patient.nurse?.id,
            patientStartDate : patient.startDate,
            patientEndDate : patient.endDate,
            patientDrugRegimeId: patient.regime?.id
    )

}

static constraints = {


}
}


@grails.validation.Validateable(nullable=false)
class StepOneCommand implements Serializable{

String patientName //wont be editable

Long patientDoctorId  //user id of assigned doctor
Long patientNurseId   //user id of assigned doctor

Date patientStartDate
Date patientEndDate

Long patientDrugRegimeId

static constraints = {
    patientDoctorId(nullable: false)
    patientNurseId(nullable: false)
    patientStartDate(nullable: false)
    patientEndDate(nullable: false)
    patientDrugRegimeId(nullable: false)
}
}


@grails.validation.Validateable(nullable=false)
class StepTwoCommand implements Serializable{

static constraints = {

}
}

Heres my flow inside my controller:

    def newEditFlow = {

    init {
        //start the flow by transferring domain obj into a command object
        action {
            Patient patient = Patient.get(params.id)
            [patientEditFlowCommand:new PatientEditFlowCommand(patient)]
            success()
        }
        on ("success"){

        }.to "stepOne"

    }

    stepOne{

        on("next") {

        }.to("stepTwo")

        on("cancel").to("finish")

    }

    stepTwo{

        on("next") {

        }.to("stepThree")

        on("previous").to("stepOne")
    }

    stepThree{

        on("next") {

        }.to("stepFour")

        on("previous").to("stepTwo")
    }

    stepFour{

        on("next") {

        }.to("finish")

        on("previous").to("stepThree")
    }

    finish{
        redirect(controller:'patient',action: "list")
    }
}

but when i navigate to the first transtion I get this

Error 500: Internal Server Error

URI /ivfportal/patient/newEdit/3 Class java.lang.NullPointerException Message null Around line 74 of GrailsFlowExecutorImpl.java

71: }72:73: try {74: return super.resumeExecution(flowExecutionKey, context);75: }76: catch (FlowExecutionRestorationFailureException e) {77: if (e.getCause() instanceof SnapshotUnmarshalException) { Around line 53 of GrailsFlowHandlerAdapter.java

50: request.setAttribute(GrailsApplicationAttributes.CONTROLLER, controllerInstance);51: }52:53: return super.handle(request, response, handler);54: }55:56: public void setGrailsApplication(GrailsApplication grailsApplication) { Around line 189 of PageFragmentCachingFilter.java

186: if (method == null) {187: log.debug("No cacheable method found for {}:{} {}",188: new Object[] { request.getMethod(), request.getRequestURI(), getContext() });189: chain.doFilter(request, response);190: return;191: }192: Collection cacheOperations = cacheOperationSource.getCacheOperations( Around line 63 of AbstractFilter.java

60: try {61: // NO_FILTER set for RequestDispatcher forwards to avoid double gzipping62: if (filterNotDisabled(request)) {63: doFilter(request, response, chain);64: }65: else {66: chain.doFilter(req, res); Around line 45 of DevModeSanityFilter.groovy

42: response.contentType = "text/html"43: response.writer << RELOADING_DOC44: } else {45: chain.doFilter(request, response)46:47: if (request.getAttribute('resources.need.layout')) {48: def dispositionsLeftOver = DispositionsUtils.getRequestDispositionsRemaining(request) Around line 53 of GrailsAnonymousAuthenticationFilter.java

50:51: applyAnonymousForThisRequest((HttpServletRequest)req);52:53: chain.doFilter(req, res);54: }55:56: protected void applyAnonymousForThisRequest(HttpServletRequest request) { Around line 139 of RestAuthenticationFilter.groovy

anyone se where I'm going wrong ? Is there a simpler but still tidy way of collecting data over a multi page flow in Grails ?