code: public void setReadAccess(String userId, boolean allowed) {
      if (StringUtil.isEmpty(userId)) {
        throw new IllegalArgumentException("cannot setRead/WriteAccess for null userId");
      }
      boolean writePermission = getWriteAccess(userId);
      setPermissionsIfNonEmpty(userId, allowed, writePermission);
    }
docs: Set whether the given user id is allowed to read this object.