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