code: public static boolean canBeDeleted (@Nullable final IUser aUser)
    {
      return aUser != null && !aUser.isDeleted () && !aUser.isAdministrator ();
    }
docs: Check if a user can be deleted or not. Currently all not deleted users can
  be deleted except for the administrator special user.
  
  @param aUser
  The user to check. May be <code>null</code>.
  @return <code>true</code> if the user can be deleted, <code>false</code> if
  not.