fixed 谭 domain bug in development environment.

app/helpers/application_helper.rb

@@ -1500,7 +1500,7 @@ module ApplicationHelper
   end
 
   def render_dynamic_nav
-    home_link = link_to l(:field_homepage), "http://"+Setting.forge_domain+":3000"
+    home_link = link_to l(:field_homepage), Setting.forge_domain.nil? ? nil : "http://"+Setting.forge_domain+":3000"
     course_all_course_link = link_to l(:label_course_all), {:controller => 'projects', :action => 'course', :project_type => 1,}
     course_teacher_all_link = link_to l(:label_teacher_all), {:controller => 'users', :action => 'index', :role => 'teacher'}
     courses_link = link_to l(:label_course_practice), {:host=>Setting.course_domain}