private void persistRequirementsAsJSON(SortedMap<String, Requirement> requirementsByPath) {
   try {
     persister.write(requirementsByPath);
   } catch (IOException e) {
     e.printStackTrace();
   }
 }
 private SortedMap<String, Requirement> loadFromJSON() {
   try {
     return persister.read();
   } catch (IOException e) {
     e.printStackTrace();
     return new TreeMap<String, Requirement>();
   }
 }