I need to get process variables via REST in JSON

i'm using standard API with Accept header "application/json"

kie-server/services/rest/server/containers/CONTAINER_NAME/processes/instances/PROCESS_ID/variables

It usually works fine but sometimes i need to tweak ObjectMapper to work with empty beans:

objectMapper.configure( SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS, false );

How can I configure to JBPM object mapper?