code: private StorageService verifyStorageServiceOption(ApplicationDefinition currAppDef, ApplicationDefinition appDef) {
          // Verify or assign StorageService
          String ssName = getStorageServiceOption(appDef);
          StorageService storageService = getStorageService(appDef);
          Utils.require(storageService != null, "StorageService is unknown or hasn't been initialized: %s", ssName);
          
          // Currently, StorageService can't be changed.
          if (currAppDef != null) {
              String currSSName = getStorageServiceOption(currAppDef);
              Utils.require(currSSName.equals(ssName), "'StorageService' cannot be changed for application: %s", appDef.getAppName());
          }
          return storageService;
      }
docs: change, ensure it hasn't changed.  Return the application's StorageService object.