Custom Http Task Behaviour

I am using spring boot based flowable bpmn engine. I am using http task

I observed that if we set saveResponseVariableAsJson as true and response status code as non 200 alongwith non JSON response handleStatusCode not working. Because in BaseHttpActivityDelegate::saveResponseFields method response is parsed before handleStatusCode logic which does not reach anyway as exception already occurred. In my opinion response status code should be processed before parsing response body; many times 500 response is returned by service with html response body.
To achieve this I have added custom HttpActivityBehaviorImpl where I did change in sequence as mentioned above and specifying that as extensionElement of http Service task.

But this <flowable:field name=“httpActivityBehaviorClass”> class does not accept DelegateExpression like other service task. So I can’t use spring bean.
Incase I use delegateExpression what should I write in execute method. I need customized saveResponseFields here in this bean.