CRM 365: Fetch Xml and Layout Xml for Link Entity attribute - Does not display link entity attributes in the sub grid

Hi, 
I'm using Dynamics 365 and build a custom fetch xml for a sub grid

The link entity attributes are not displayed in the sub grid

Maybe you have a clue fro me?

Thanks

fetchXml = "<fetch version='1.0' output-format='xml-platform' mapping='logical' distinct='false'>" +
                           "  <entity name='hr_assignment'>" +
                           "    <attribute name='hr_assignmentid' />" +
                           "    <attribute name='hr_name' />" +
                           "    <attribute name='hr_standard_id' />" +
                           "        <filter type='and'>" +
                           "          <condition attribute='hr_tribunalid' operator='eq' uitype='hr_tribunal' value='" + Xrm.Page.data.entity.getId() + "' />" +
                           "          <condition attribute='hr_assignment_status' operator='eq' value='315840002' />" +
                           "          <condition attribute='hr_standard_id' operator='not-null' />" +
                           "        </filter>" +
                           "    <link-entity name='hr_judges' from='hr_judgesid' to='hr_judgeid' alias='a' link-type='outer' >" +
                           "       <attribute name='hr_lastname' />" +
                           "       <attribute name='hr_firstname' />" +
                           "    </link-entity>" +
                           "    <link-entity name='hr_standard' from='hr_standardid' to='hr_standard_id' alias='b' link-type='outer'>" +
                           "       <attribute name='hr_judge_role_id' />" +
                           "       <attribute name='statuscode' />" +
                           "    </link-entity>" +
                           "  </entity>" +
                           "</fetch>";

var LayoutXml = "<grid name='resultset' object='8' jump='hr_name' select='1' preview='1' icon='1'>" +
                " <row name='result' id='hr_assignment'>" +
                     "<cell name='hr_assignmentid' width='50' />" +
                     "<cell name='hr_name' width='100' />" +
                     "<cell name='hr_standard_id' width='50' />" +
                     "<cell name='a.hr_lastname' width='50' />" +
                     "<cell name='a.hr_firstname' width='100' />" +
                     "<cell name='b.hr_judge_role_id' width='50' />" +
                     "<cell name='b.statuscode' width='100' />" +
                "</row>" +
             "</grid>";

objSubGrid.control.SetParameter("layoutXml", LayoutXml);
objSubGrid.control.SetParameter("fetchXml", fetchXml);
objSubGrid.control.Refresh();