Update lectures_controller.rb

If a lecture had no editors the old code would perform actions on a nil object causing an error.
Now the relevant passage in the update method is surrounded by an if-statement which first checks, if the given array of editor ids is nil and skips the passage in this case.

app/controllers/lectures_controller.rb

@@ -26,20 +26,23 @@ def edit
   end
 
   def update
-    # removes the empty String "" in the NEW array of editor ids
-    # and converts it into an array of integers
-    all_ids = lecture_params[:editor_ids].map(&:to_i) - [0]
-    old_ids = @lecture.editor_ids
-    new_ids = all_ids - old_ids
-
-    # returns an array of Users that match the given ids
-    recipients = User.where(id: new_ids)
-
-    recipients.each do |r|
-      NotificationMailer.with(recipient: r,
-                              locale: r.locale,
-                              lecture: @lecture)
-                        .new_editor_email.deliver_later
+    editor_ids = lecture_params[:editor_ids]
+    if editor_ids != nil
+      # removes the empty String "" in the NEW array of editor ids
+      # and converts it into an array of integers
+      all_ids = editor_ids.map(&:to_i) - [0]
+      old_ids = @lecture.editor_ids
+      new_ids = all_ids - old_ids
+
+      # returns an array of Users that match the given ids
+      recipients = User.where(id: new_ids)
+
+      recipients.each do |r|
+        NotificationMailer.with(recipient: r,
+                                locale: r.locale,
+                                lecture: @lecture)
+                          .new_editor_email.deliver_later
+      end
     end
 
     @lecture.update(lecture_params)