diff -urN ../roundcube-thunderbird_labels-1.3.0.orig/tb_label_contextmenu.js ./tb_label_contextmenu.js
--- ../roundcube-thunderbird_labels-1.3.0.orig/tb_label_contextmenu.js	2018-09-10 19:52:53.000000000 +0300
+++ ./tb_label_contextmenu.js	2018-12-03 20:06:34.268622000 +0200
@@ -11,7 +11,7 @@
           if (p.ref.list_object) {
             prev_display_next = rcmail.env.display_next;
             list_obj = rcmail[p.ref.list_object];
-            if (!(list_obj.selection.length === 1 && list_obj.in_selection(rcmail.env.context_menu_source_id))) {
+            if (list_obj && !(list_obj.selection.length === 1 && list_obj.in_selection(rcmail.env.context_menu_source_id))) {
               rcmail.env.display_next = false;
             }
           }