internal void PopGroup()
{
_concatenation = _stack;
_alternation = _concatenation._next;
_group = _alternation._next;
_stack = _group._next;
// The first () inside a Testgroup group goes directly to the group
if (_group.Type() == RegexNode.Testgroup && _group.ChildCount() == 0)
{
if (_unit == null)
throw MakeException(SR.IllegalCondition);
_group.AddChild(_unit);
_unit = null;
}
}