Why does field_get_items() sometimes return "blank"
Reading the function's source code it seems that the only way to return 'blank' is when the field's value for the selected langcode is actually 'blank':

https://api.drupal.org/api/drupal/modules%21field%21field.module/function/field_get_items/7

I suggest you to use XDdebug to check the node_object value just before this function is called. You can also use a dirty-and-quick trick: edit the code function and add a dpm (but remember to revert it!). But with XDebug you really can see where that 'blank' value comes from.