Handle non-existing groups in register object view

CHANGELOG.rst

@@ -14,6 +14,11 @@ Changed
 
 * Use start date of current SchoolTerm as default value for PersonalNote filter in overview.
 
+Fixed
+~~~~~
+
+* Events without groups caused an error when not accessed through the week view.
+
 `2.0rc7` - 2021-12-25
 ---------------------
 

aleksis/apps/alsijil/templates/alsijil/class_register/lesson.html

@@ -50,7 +50,7 @@
   {% has_perm "alsijil.edit_lessondocumentation_rule" user register_object as can_edit_lesson_documentation %}
   {% has_perm "alsijil.edit_register_object_personalnote_rule" user register_object as can_edit_register_object_personalnote %}
 
-  {% if next_lesson_person or prev_lesson_person or lesson_documentation %}
+  {% if next_lesson_person or prev_lesson_person or back_to_week_url %}
     <div class="row margin-bottom z-depth-1 alsijil-nav-header">
       <div class="col s12 no-padding">
         {# Back to week view #}

aleksis/apps/alsijil/views.py

@@ -293,7 +293,7 @@ def register_object(
         )
         if back_url_is_safe:
             context["back_to_week_url"] = back_url
-        else:
+        elif register_object.get_groups().all():
             context["back_to_week_url"] = reverse(
                 "week_view_by_week",
                 args=[