Expose avatar URL for groups

app/helpers/groups_helper.rb

@@ -8,7 +8,7 @@ module GroupsHelper
       group = Group.find_by_full_path(group)
     end
 
-    group.try(:avatar_url) || image_path('no_group_avatar.png')
+    group.try(:avatar_url) || ActionController::Base.helpers.image_path('no_group_avatar.png')
   end
 
   def group_title(group, name = nil, url = nil)

app/serializers/group_entity.rb

@@ -2,9 +2,9 @@ class GroupEntity < Grape::Entity
   include ActionView::Helpers::NumberHelper
   include RequestAwareEntity
   include MembersHelper
+  include GroupsHelper
 
   expose :id, :name, :path, :description, :visibility
-  expose :avatar_url
   expose :web_url
   expose :full_name, :full_path
   expose :parent_id
@@ -39,4 +39,8 @@ class GroupEntity < Grape::Entity
   expose :number_users_with_delimiter do |group|
     number_with_delimiter(group.users.count)
   end
+
+  expose :avatar_url do |group|
+    group_icon(group)
+  end
 end