LM should should not try to add folder to project

Description

Steps to reproduce

1. Add a property to a Standard Page.

   [Display(

   GroupName = SystemTabNames.Content,

   Order = 400)]

   [CultureSpecific]

   public virtual ContentReference MyContentFolder { get; set; }

2. Create a Standard Page.
3. Select a folder as value of the property.
4. From LM, add to a translation project, check "Add children" and "Add related contents".

Expected:
You can add a page to a translation project

Actual:
Error on console. The page cannot be added to the translation project.