code: private Session loadSession(String id) throws Exception {
          if (sessionDataStore == null) {
              return null; // can't load it
          }
          try {
              SessionData data = sessionDataStore.load(id);
              if (data == null) { // session doesn't exist
                  return null;
              }
              return newSession(data);
          } catch (UnreadableSessionDataException e) {
              // can't load the session, delete it
              if (isRemoveUnloadableSessions()) {
                  sessionDataStore.delete(id);
              }
              throw e;
          }
      }
docs: Load the info for the session from the session data store.
  
  @param id the session id
  @return a Session object filled with data or null if the session doesn't exist
  @throws Exception if the session can not be loaded