docs: private UserRegistry determineActiveUserRegistry(boolean exceptionOnError) throws RegistryException {
          synchronized (userRegistrySync) {
              UserRegistry ur = userRegistry.get();
              if (ur == null) {
                  if (isConfigured()) {
                      ur = getUserRegistryFromConfiguration();
                  } else {
                      ur = autoDetectUserRegistry(exceptionOnError);
                  }
  
                  // remember the user registry to use
                  userRegistry.set(ur);
              }
              return ur;
          }
      }