Error when adding a collection attribute to a CMS Component

Dear experts, et al.,

I created a collection of countries:

 <collectiontype code="RestrictedCountries" elementtype="Country" type="set"/>

And then I modified an OOTB CMS component called CMSNavigationNode in the following way:

     <itemtype code="CMSNavigationNode" generate="false" autocreate="false">
         <attributes>
             <attribute type="RestrictedCountries" qualifier="restrictedCountries">
                 <persistence type="property" />
             </attribute>
         </attributes>
     </itemtype>

I also modified editorArea_CMSNavigationNode.xml to ensure my new attribute shows up.

 ...
         <property qualifier="cmsnavigationnode.restrictedCountries">
             <parameter>
                 <name>predefinedValuesStrategy</name>
                 <value>cmsItemPredefinedValuesStrategy</value>
             </parameter>
         </property>
 ...

The Problem that I have is when I try to use it, it gives me the following error message:

 Caused by: de.hybris.platform.jalo.flexiblesearch.FlexibleSearchException: cannot search unknown field 'TableField(name='uid',langPK='null',
 type=Country)' within type Country unless you disable checking , infoMap=TypeInfoMap for type = 8796101869650
    code = Country

I am attaching the whole error message (link text) in case that you would be so kind to look into it.

Any help will be greatly appreciated!

Kind regards,

L