docs: @Nonnull
      public UserDetails loadUserByUsername(String idOrFullName) throws UsernameNotFoundException, DataAccessException, ExecutionException {
          Boolean exists = existenceCache.getIfPresent(idOrFullName);
          if(exists != null && !exists) {
              throw new UsernameNotFoundException(String.format("\"%s\" does not exist", idOrFullName));
          } else {
              try {
                  return detailsCache.get(idOrFullName, new Retriever(idOrFullName));
              } catch (ExecutionException | UncheckedExecutionException e) {
                  if (e.getCause() instanceof UsernameNotFoundException) {
                      throw ((UsernameNotFoundException)e.getCause());
                  } else if (e.getCause() instanceof DataAccessException) {
                      throw ((DataAccessException)e.getCause());
                  } else {
                      throw e;
                  }
              }
          }
      }