docs: private static String getFileName(@Nullable final MapPrinter mapPrinter, final PJsonObject spec) {
          String fileName = spec.optString(Constants.OUTPUT_FILENAME_KEY);
          if (fileName != null) {
              return fileName;
          }
  
          if (mapPrinter != null) {
              final Configuration config = mapPrinter.getConfiguration();
              final String templateName = spec.getString(Constants.JSON_LAYOUT_KEY);
  
              final Template template = config.getTemplate(templateName);
  
              if (template.getOutputFilename() != null) {
                  return template.getOutputFilename();
              }
  
              if (config.getOutputFilename() != null) {
                  return config.getOutputFilename();
              }
          }
          return "mapfish-print-report";
      }