I have a custom theme (subtheme of drupal bootstrap theme).  We are overriding `menu--account.html.twig`.  So I copied `menu--account.html.twig` from the bootstrap theme template folder into my theme's template folder, and I verified this template is being used because static text changes I added show up on screen.  

Now I'm trying to add a variable that the `menu--account.html.twig` template can read.

How do I do that?  My variable's name is 'nickname'.  I tried this:

     function mymodule_preprocess_menu__account(&$variables)
     {     
         $variables['nickname'] = 'Jeff';     
     }  

The variable is added to the array, and I can see it if I use dpm, but when I reference {{nickname}} in the template it's always null.

I also read I had to define the variable like this:

     function candidate_poral_theme_registry_alter(&$theme_registry)
     {
       $theme_registry['menu__account']['variables']['nickname'] = 'default';
     }

But that also doesn't work.  

Any assistance would be welcome.