Flowr: Return empty array if no submission was found

app/controllers/flowr_controller.rb

@@ -6,6 +6,14 @@ class FlowrController < ApplicationController
     submission = Submission.joins(:testruns)
                      .where(submissions: {user_id: current_user.id, user_type: current_user.class.name})
                      .order('testruns.created_at DESC').first
+
+    # Return if no submission was found
+    if submission.blank?
+      skip_authorization
+      render json: [], status: :ok
+      return
+    end
+
     # verify authorization for the submission, as all queried errors are generated by this submission anyway
     # and structured_errors don't have a policy yet
     authorize(submission)