use safe_join

lib/redmine_qbo/hooks/view_hook_listener.rb

@@ -15,10 +15,11 @@ module RedmineQbo
 
       # Load the javascript to support the autocomplete forms
       def view_layouts_base_html_head(context = {})
-        js = javascript_include_tag 'application.js', plugin: :redmine_qbo
+        safe_join([
-        js += javascript_include_tag 'autocomplete-rails.js', plugin: :redmine_qbo
+          javascript_include_tag( 'application.js', plugin: :redmine_qbo),
-        js += javascript_include_tag 'checkbox_controller.js', plugin: :redmine_qbo
+          javascript_include_tag( 'autocomplete-rails.js', plugin: :redmine_qbo),
-        return js
+          javascript_include_tag( 'checkbox_controller.js', plugin: :redmine_qbo)
+        ])
       end
 
       render_on :view_layouts_base_sidebar, partial: "qbo/sidebar"