code: public T payload(Object payload, ObjectMapper objectMapper) {
          try {
              setPayload(objectMapper.writer().writeValueAsString(payload));
          } catch (JsonProcessingException e) {
              throw new CitrusRuntimeException("Failed to map object graph for message payload", e);
          }
  
          return self;
      }
docs: Expect this message payload as model object which is mapped to a character sequence
  using the default object to json mapper before validation is performed.
  @param payload
  @param objectMapper
  @return