fix show

app/policies/learning_object_policy.rb

@@ -36,7 +36,7 @@ class LearningObjectPolicy < ApplicationPolicy
   end
 
   def show?
-    return record if record.published? || user.is_admin?
+    return record if record.published? || user.try(:is_admin?)
     return record if user == record.publisher
     ## TODO: falta verificar se o +record.publisher+ é uma instituição e +user+ faz parte
   end
@@ -44,7 +44,7 @@ class LearningObjectPolicy < ApplicationPolicy
   def index?
     record
   end
-  
+
   def add_object?
     record if user_exists?
   end