Merge pull request activeadmin#3398 from timoschilling/site_title

fix empty site_title case

Author: seanlinsley

lib/active_admin/views/pages/base.rb

@@ -22,7 +22,7 @@ def add_classes_to_body
 
         def build_active_admin_head
           within @head do
-            insert_tag Arbre::HTML::Title, [title, render_or_call_method_or_proc_on(self, active_admin_namespace.site_title)].join(" | ")
+            insert_tag Arbre::HTML::Title, [title, render_or_call_method_or_proc_on(self, active_admin_namespace.site_title)].compact.join(" | ")
             active_admin_application.stylesheets.each do |style, options|
               text_node stylesheet_link_tag(style, options).html_safe
             end