diff --git a/app/controllers/dmsf_folder_permissions_controller.rb b/app/controllers/dmsf_folder_permissions_controller.rb
index 4b30fe8a..85765a44 100644
--- a/app/controllers/dmsf_folder_permissions_controller.rb
+++ b/app/controllers/dmsf_folder_permissions_controller.rb
@@ -53,8 +53,10 @@ class DmsfFolderPermissionsController < ApplicationController
     scope = Principal.active.visible.member_of(@project).like(params[:q]).order(:type, :lastname)
     if @dmsf_folder
       users = @dmsf_folder.permissions_users
-      ids = users.collect{ |u| u.id }
-      scope = scope.where(['id NOT IN (?)', ids.join(',')]).order(:type, :lastname)
+      if(users.any?)
+        ids = users.collect{ |u| u.id }
+        scope = scope.where.not(id: ids)
+      end
     end
     scope.to_a
   end
diff --git a/app/helpers/dmsf_folder_permissions_helper.rb b/app/helpers/dmsf_folder_permissions_helper.rb
index dce45bba..c73202c0 100644
--- a/app/helpers/dmsf_folder_permissions_helper.rb
+++ b/app/helpers/dmsf_folder_permissions_helper.rb
@@ -23,7 +23,7 @@
 module DmsfFolderPermissionsHelper
 
   def users_checkboxes(users, inherited = false)
-    s = ''
+    s = +''
     id = inherited ? 'inherited_permissions[user_ids][]' : 'permissions[user_ids][]'
      users.each do |user|
       content = check_box_tag(id, user.id, true, disabled: inherited, id: nil) + user.name