fix when roles is nil

Signed-off-by: Alexandre Arias <apa13@inf.ufpr.br>

app/controllers/management/users_controller.rb

@@ -76,7 +76,9 @@ class Management::UsersController < ManagementController
     @curators = Array.new
     @users = User.includes(:roles).all
     @users.all.each do |user|
-     @curators << user if user.roles[0].name == "curator"
+      if !user.roles[0].nil?
+        @curators << user if user.roles[0].name == "curator" || []
+      end
     end
   end
 
@@ -84,7 +86,9 @@ class Management::UsersController < ManagementController
     @admins = Array.new
     @users = User.includes(:roles).all
     @users.all.each do |user|
-      @admins << user if user.roles[0].name == "admin"
+      if !user.roles[0].nil?
+        @admins << user if user.roles[0].name == "admin" || []
+      end
     end
   end