Error when getting a primitive type process instance variable when using the REST API

process with variables of primitive types is started and when we try to retrieve this processes variables using the REST API, we have marshalling errors, such as:

16:14:38,054 WARN [org.kie.remote.services.rest.exception.DescriptiveExceptionHandler] (http-localhost.localdomain/127.0.0.1:8080-5) Exception thrown when processing request [/runtime/com.redhat.consulting:TestProj:1.0/process/instance/4/variable/myVar]; responding with status 500: org.kie.remote.services.rest.exception.RestOperationException: Unable to serialize java.lang.String instance because it is missing a javax.xml.bind.annotation.XmlRootElement annotation with a name value.

Endpoint: rest/runtime/PROCESS/process/instance/INSTANCE ID/variable/VAR_NAME
It is not happening with complex types, only with primitive types: boolean, float, integer and String.

Found that the Java implementation of this REST resource always treat the variable as a complex object and try to marshal it:

    @GET
    @Path("/process/instance/{procInstId: [0-9]+}/variable/{varName: [\\w\\.-]+}")
    public Response process_instance_procInstId_variable_varName(@PathParam("procInstId") Long procInstId,
            @PathParam("varName") String varName) {
        Object procVar =  processRequestBean.getVariableObjectInstanceFromRuntime(deploymentId, procInstId, varName);
    
        // serialize
        QName rootElementName = getRootElementName(procVar); 
        @SuppressWarnings("rawtypes") // unknown at compile time, dynamic from deployment
        JAXBElement<?> jaxbElem = new JAXBElement(rootElementName, procVar.getClass(), procVar) ;
    
        // return
        return createCorrectVariant(jaxbElem, headers);
    }