membershipworks: Handle events without instructors better

membershipworks/models.py

@@ -556,6 +556,8 @@ class EventExt(Event):
         return reverse("membershipworks:event-detail", kwargs={"eid": self.eid})
 
     def user_is_instructor(self, user: AbstractBaseUser) -> bool:
+        if self.instructor is None:
+            return False
         member = Member.from_user(user)
         if member is not None:
             return self.instructor.member == member

membershipworks/templates/membershipworks/event_invoice.dj.html

@@ -55,6 +55,11 @@
   <div class="vr d-none d-md-block m-4 p-0"></div>
   <div class="col-12 col-md-4">
     <div>
+      {% if event.instructor is None %}
+        <div>No instructor has been defined for this event</div>
+      {% elif event.instructor.member is None %}
+        <div>Instructor is not a member, so no address information is known</div>
+      {% else %}
         <h3>From:</h3>
         <div>{{ event.instructor.member.account_name }}</div>
         <div>{{ event.instructor.member.address_street }}</div>
@@ -65,6 +70,7 @@
         </div>
         <div>{{ event.instructor.member.email }}</div>
         <div>{{ event.instructor.member.phone }}</div>
+      {% endif %}
     </div>
   </div>
 </div>