code: private void setupAcceptHeader(String action, Map<String, String> requestHeaders, Map<String, String> requestParameters) {
          // validates whether to add headers for accept for serialization
          String serializeAcceptFormat = getSerializationResponseFormat();
          if (StringUtils.hasText(serializeAcceptFormat)
                  && !isDownload(action)
                  && !isDownloadPDF(requestParameters)) {
                       requestHeaders.put(RequestElements.HEADER_PARAM_ACCEPT, ContentTypes.getContentType(serializeAcceptFormat));
          }
  
          if(isDownloadPDF(requestParameters)) {
              requestHeaders.put(RequestElements.HEADER_PARAM_ACCEPT, ContentTypes.getContentType(requestParameters.get(RequestElements.REQ_PARAM_ENTITY_SELECTOR)));
          }
      }
docs: Setup accept header depends from the semantic of the request
  @param action
  @param requestHeaders