show_user_name.xml

<!--Do a look-up and find the First Name of the current user -->
<g:evaluate>
 var name  = gs.getUser().getFirstName()
   if(name == ''){
      <!--If there is no value for First Name, then query the sys_user table and get the user_name value -->
   var usr = new GlideRecord('sys_user');
    usr.get(gs.getUserID());
   name = usr.user_name.getDisplayValue()
}
if(name == ''){
name ="empty";
}
</g:evaluate>

<!-- Wrap the actual value however you choose (i.e. H3 or p tags) -->
<div class="user_name">
  ${name}
</div>