Upgrade DatabaseCleaner strategy

app/controllers/concerns/submission_parameters.rb

@@ -14,14 +14,10 @@ module SubmissionParameters
   private :submission_params
 
   def merge_user(params)
-    if current_user
-      current_user_id = current_user.id
-      current_user_class_name = current_user.class.name
-    end
     # The study_group_id might not be present in the session (e.g. for internal users), resulting in session[:study_group_id] = nil which is intended.
     params.merge(
-      user_id: current_user_id,
-      user_type: current_user_class_name,
+      user_id: current_user.id,
+      user_type: current_user.class.name,
       study_group_id: session[:study_group_id]
     )
   end

app/controllers/exercises_controller.rb

@@ -500,8 +500,7 @@ class ExercisesController < ApplicationController
   def submit
     @submission = Submission.create(submission_params)
     score_submission(@submission)
-    current_user = ExternalUser.find(@submission.user_id)
-    if !current_user.nil? && lti_outcome_service?(@submission.exercise_id, current_user.id)
+    if @submission.user.external_user? && lti_outcome_service?(@submission.exercise_id, @submission.user.id)
       transmit_lti_score
     else
       redirect_after_submit