RequestTypeFieldService implementation?

I need to get the list of fields defined on a Request Type. I assume that I use RequestTypeFieldService but I can’t find any way to instantiate it so that I can query the request type definition.

I am using ScriptRunner and have tried to instantiate using @WithPlugin and @PluginModule to instantiate the service. I get the following error in the log:

Cant find plugin module or OSGi service for class: com.atlassian.servicedesk.api.field.RequestTypeFieldQuery

Apparently, there is no implementation?

This works fine.

import com.onresolve.scriptrunner.runner.customisers.WithPlugin
import com.onresolve.scriptrunner.runner.customisers.PluginModule
import com.atlassian.servicedesk.api.requesttype.RequestTypeService
import com.atlassian.servicedesk.api.field.RequestTypeFieldService
import com.atlassian.jira.component.ComponentAccessor

@WithPlugin('com.atlassian.servicedesk')

@PluginModule
RequestTypeService requestTypeService

@PluginModule
RequestTypeFieldService requestTypeFieldService

def loggedInUser = ComponentAccessor.jiraAuthenticationContext.loggedInUser

def requestTypesForAServiceDesk = requestTypeService.getRequestTypes(
    loggedInUser,
    requestTypeService.newQueryBuilder()
        .serviceDesk(6)
        .build()
)

def oneSpecificRequestType = requestTypesForAServiceDesk.first()

def requestTypeCreateMeta = requestTypeFieldService.getCustomerRequestCreateMeta(
    loggedInUser, 
    requestTypeFieldService.newQueryBuilder()
        .serviceDesk(6)
        .requestType(oneSpecificRequestType.id)
        .build()
    )