code: @Nonnull
    @ReturnsMutableCopy
    public ICommonsList <IUserGroup> getAllUserGroupsWithAssignedUser (@Nullable final String sUserID)
    {
      if (StringHelper.hasNoText (sUserID))
        return new CommonsArrayList <> ();
  
      return getAll (aUserGroup -> aUserGroup.containsUserID (sUserID));
    }
docs: Get a collection of all user groups to which a certain user is assigned to.
  
  @param sUserID
  The user ID to search
  @return A non-<code>null</code>but may be empty collection with all
  matching user groups.