apply StringLiterals cop (remove double quotes, unless there is string interpolation)

app/controllers/admin/callforpapers_controller.rb

@@ -28,7 +28,7 @@ module Admin
       else
         redirect_to(admin_conference_callforpapers_path(
                     id: @conference.short_title),
-                    alert: "Updating call for papers failed. #{@cfp.errors.to_a.join(". ")}.")
+                    alert: "Updating call for papers failed. #{@cfp.errors.to_a.join('. ')}.")
       end
     end
 
@@ -44,7 +44,7 @@ module Admin
       else
         redirect_to(admin_conference_callforpapers_path(
                     id: @conference.short_title),
-                    alert: "Creating the call for papers failed. #{@cfp.errors.to_a.join(". ")}.")
+                    alert: "Creating the call for papers failed. #{@cfp.errors.to_a.join('. ')}.")
       end
     end
   end

app/controllers/admin/difficulty_levels_controller.rb

@@ -13,18 +13,18 @@ module Admin
           begin
             @conference.use_difficulty_levels = false
             @conference.save!
-            flash[:error] = "You cannot enable the usage of difficulty levels without having set any levels."
+            flash[:error] = 'You cannot enable the usage of difficulty levels without having set any levels.'
             redirect_to(admin_conference_difficulty_levels_path(conference_id: @conference.short_title))
           rescue ActiveRecord::RecordInvalid
-            flash[:error] = "Something went wrong. Difficulty Levels update failed."
+            flash[:error] = 'Something went wrong. Difficulty Levels update failed.'
             redirect_to(admin_conference_difficulty_levels_path(conference_id: @conference.short_title))
           end
         else
-          flash[:notice] = "Difficulty Levels were successfully updated."
+          flash[:notice] = 'Difficulty Levels were successfully updated.'
           redirect_to(admin_conference_difficulty_levels_path(conference_id: @conference.short_title))
         end
       else
-        flash[:error] = "Difficulty Levels update failed."
+        flash[:error] = 'Difficulty Levels update failed.'
         redirect_to(admin_conference_difficulty_levels_path(conference_id: @conference.short_title))
       end
     end

app/controllers/admin/questions_controller.rb

@@ -33,7 +33,7 @@ module Admin
     # GET questions/1/edit
     def edit
       if @question.global
-        redirect_to(admin_conference_questions_path(conference_id: @conference.short_title), alert: "Sorry, you cannot edit global questions. Create a new one.")
+        redirect_to(admin_conference_questions_path(conference_id: @conference.short_title), alert: 'Sorry, you cannot edit global questions. Create a new one.')
       end
     end
 
@@ -73,13 +73,13 @@ module Admin
               flash[:notice] = "Deleted question: #{@question.title} and its answers: #{@question.answers.map {|a| a.title}.join ','}"
             end
           rescue ActiveRecord::RecordInvalid
-            flash[:error] = "Could not delete question."
+            flash[:error] = 'Could not delete question.'
           end
         else
-          flash[:error] = "You cannot delete global questions."
+          flash[:error] = 'You cannot delete global questions.'
         end
       else
-        flash[:error] = "You must be an admin to delete a question."
+        flash[:error] = 'You must be an admin to delete a question.'
       end
 
       @questions = Question.where(global: true).all | Question.where(conference_id: @conference.id)

app/controllers/admin/supporters_controller.rb

@@ -0,0 +1,19 @@
+module Admin
+  class SupportersController < Admin::BaseController
+    load_and_authorize_resource :conference, find_by: :short_title
+    load_and_authorize_resource through: :conference
+
+    def index
+      respond_to do |format|
+        format.html
+        format.json { render json: DatatableSupporters.new(@conference.supporter_registrations, view_context) }
+      end
+    end
+
+    def create
+      params[:supporter_registration][:conference_id] = @conference.id
+      SupporterRegistration.create!(params[:supporter_registration])
+      redirect_to(admin_conference_supporters_path(conference_id: @conference.short_title), notice: 'Supporter added')
+    end
+  end
+end

app/controllers/admin/volunteers_controller.rb

@@ -25,7 +25,7 @@ module Admin
     def update
       if can_manage_volunteers(@conference)
         if @conference.update_attributes(params[:conference])
-          redirect_to(admin_conference_volunteers_info_path(conference_id: params[:conference_id]), notice: "Volunteering options were successfully updated.")
+          redirect_to(admin_conference_volunteers_info_path(conference_id: params[:conference_id]), notice: 'Volunteering options were successfully updated.')
         else
           redirect_to(admin_conference_volunteers_info_path(conference_id: params[:conference_id]), alert: "Volunteering options update failed: #{@conference.errors.full_messages.join '. '}")
         end