Do not raise error in AutocompleteController#users when not authorized

https://gitlab.com/gitlab-org/gitlab-ce/issues/25031

app/controllers/autocomplete_controller.rb

@@ -11,7 +11,7 @@ class AutocompleteController < ApplicationController
     @users = @users.reorder(:name)
     @users = @users.page(params[:page])
-    if params[:todo_filter].present?
+    if params[:todo_filter].present? && current_user
       @users = @users.todo_authors(current_user.id, params[:todo_state_filter])
     end

changelogs/unreleased/25031-do-not-raise-error-in-autocomplete.yml

+---
+title: Do not raise error in AutocompleteController#users when not authorized
+merge_request: 7817
+author: Semyon Pupkov

spec/controllers/autocomplete_controller_spec.rb

@@ -144,6 +144,15 @@ describe AutocompleteController do
         it { expect(body).to be_kind_of(Array) }
         it { expect(body.size).to eq 0 }
       end
+
+      describe 'GET #users with todo filter' do
+        it 'gives an array of users' do
+          get :users, todo_filter: true
+
+          expect(response.status).to eq 200
+          expect(body).to be_kind_of(Array)
+        end
+      end
     end
     context 'author of issuable included' do