docs: @Nonnull
    public EChange disableUser (@Nullable final String sUserID)
    {
      final User aUser = getOfID (sUserID);
      if (aUser == null)
      {
        AuditHelper.onAuditModifyFailure (User.OT, sUserID, "no-such-user-id", "disable");
        return EChange.UNCHANGED;
      }
  
      m_aRWLock.writeLock ().lock ();
      try
      {
        if (aUser.setDisabled (true).isUnchanged ())
          return EChange.UNCHANGED;
        internalUpdateItem (aUser);
      }
      finally
      {
        m_aRWLock.writeLock ().unlock ();
      }
      AuditHelper.onAuditModifySuccess (User.OT, "disable", sUserID);
  
      // Execute callback as the very last action
      m_aCallbacks.forEach (aCB -> aCB.onUserEnabled (aUser, false));
  
      return EChange.CHANGED;
    }