public override void VisitNameMemberCref(NameMemberCrefSyntax node)
                {
                    base.VisitNameMemberCref(node);
                    var sym = parent.semanticModel.GetSymbolInfo(node).Symbol;

                    if (sym == null)
                    {
                        parent.AddXmlIssue(node.Span.Start, node.Span.Length, string.Format(GettextCatalog.GetString("Cannot find reference '{0}'"), node.Name));
                    }
                }