@Nullable abstract fun handleEmptyBody(@Nullable body: Any, inputMessage: HttpInputMessage, parameter: MethodParameter, targetType: Type, converterType: Class<out HttpMessageConverter<*>>): Any
Invoked second (and last) if the body is empty.
body - usually set to null before the first advice is called
parameter - the method parameter
targetType - the target type, not necessarily the same as the method parameter type, e.g. for HttpEntity<String>.
converterType - the selected converter type
Return
the value to use or null which may then raise an HttpMessageNotReadableException if the argument is required.