code: public RequestBuilder createFileUploadRequestBuilder(String httpUrl, String methodName, String reqBodyAsString) throws IOException {
          Map<String, Object> fileFieldNameValueMap = getFileFieldNameValue(reqBodyAsString);
  
          List<String> fileFieldsList = (List<String>) fileFieldNameValueMap.get(FILES_FIELD);
  
          MultipartEntityBuilder multipartEntityBuilder = MultipartEntityBuilder.create();
  
          /*
  	 * Allow fileFieldsList to be null.
  	 * fileFieldsList can be null if multipart/form-data is sent without any files
  	 * Refer Issue #168 - Raised and fixed by santhoshTpixler
  	 */
          if(fileFieldsList != null) {
          	buildAllFilesToUpload(fileFieldsList, multipartEntityBuilder);
  	}
  
          buildOtherRequestParams(fileFieldNameValueMap, multipartEntityBuilder);
  
          buildMultiPartBoundary(fileFieldNameValueMap, multipartEntityBuilder);
  
          return createUploadRequestBuilder(httpUrl, methodName, multipartEntityBuilder);
      }
docs: This is the http request builder for file uploads, using Apache Http Client. In case you want to build
  or prepare the requests differently, you can override this method.
  
  Note-
  With file uploads you can send more headers too from the testcase to the server, except "Content-Type" because
  this is reserved for "multipart/form-data" which the client sends to server during the file uploads. You can
  also send more request-params and "boundary" from the test cases if needed. The boundary defaults to an unique
  string of local-date-time-stamp if not provided in the request.
  
  You can override this method via @UseHttpClient(YourCustomHttpClient.class)
  
  @param httpUrl
  @param methodName
  @param reqBodyAsString
  @return
  @throws IOException