How do I make a panel visibility rule work when the element to check for has to be not set or empty? I am using Drupal 7, panels and page manager modules.

In page manager I created variants on the node template for showing a particular type of node in a different fashion to different user roles. My nodes have a Term Reference field called "Alternatives" that is NOT required to be set by the users so it can be either be "empty" aka "none" or set to some data value i.e. a taxonomy term of the vocabulary "Alternatives". 

I created a visibility rule on another element on the same variant to hide this "other" element, a custom content.

From the element's gear icon (on the tab "Content" in the variant section) of the custom content, I have set the visibility rule to show: Alternatives is set to "". That's exactly what I want: if Alternatives is set to "nothing", this custom content should show and now it doesn't show.

It seems that the visibility rule doesn't seem to recognise or can't check if a term reference field (Alternatives) is empty or not set. How do I make this visibility rule work?
use flags module, and rules module, make a rule when save/update your content type, condition: your_field_value is empty, if true, flag your node, then in panels add your panels-rule visibility  based on your new flag.