Can not use Content-type in header to change HttpMessageConvert

would like to move addHeaderMapHeaders before the method resolve?

   public RequestTemplate create(Object[] argv) {
      ......
      RequestTemplate template = resolve(argv, mutable, varBuilder);
      if (metadata.queryMapIndex() != null) {
        // add query map parameters after initial resolve so that they take
        // precedence over any predefined values
        Object value = argv[metadata.queryMapIndex()];
        Map<String, Object> queryMap = toQueryMap(value);
        template = addQueryMapQueryParameters(queryMap, template);
      }

      if (metadata.headerMapIndex() != null) {
        template =
            addHeaderMapHeaders((Map<String, Object>) argv[metadata.headerMapIndex()], template);
      }

      return template;
    }

Start in the RequestTemplate create(Object[] argv) entry point and compare the ordering of resolve and addHeaderMapHeaders shown in the issue. Trace how the Content-type header reaches HttpMessageConvert, then verify whether moving header-map processing before resolve enables the requested behavior and add a regression test if the project has a suitable location.