[erp5_hal_json_style] Do not generate link for empty value, as it will not be clickable in UI

bt5/erp5_hal_json_style/SkinTemplateItem/portal_skins/erp5_hal_json_style/ERP5Document_getHateoas.py

@@ -1814,6 +1814,8 @@ def calculateHateoas(is_portal=None, is_site_root=None, traversed_document=None,
             key='field_%s_%s' % (editable_field.id, brain_uid))
 
 
+        # Do not generate link for empty value, as it will not be clickable in UI
+        if default_field_value not in ('', None):
           # By default, we won't be generating views in the URL
           url_parameter_dict = None
           if select in url_column_dict: