raising exceptions when check_references of some user

app/repositories/user_repository_proxy.rb

@@ -40,7 +40,6 @@ class UserRepositoryProxy
     User.respond_to?(method_name) || super
   end
 
-
   private
 
   attr_reader :orientdb_user_repository
@@ -52,6 +51,14 @@ class UserRepositoryProxy
   end
 
   def check_references(user)
+    if !user.persisted?
+      raise_not_persisted_error
+    end
+
+    if user.rid.nil?
+      raise 'OrientDb reference is null'
+    end
+
     rid = get_graph_id user
     (rid == user.rid)
   end