code: function(options, callback) {
        if(typeof options === 'function') {
          callback = options;
          options = {};
        }
        if(options.items) {
          options.users = options.users || [];
          for(var i = 0; i < options.items.length ; i++){
            options.users.push(options.items[i]._key);
          }
          delete options.items;
        }
        if(options.title) {
          options.label = options.title;
          delete options.title;
        }
        if (!self.context.player || !options.users || options.users.length === 0 ) {
          callback.apply(self);
        } else {
          UT.Expression._callAPI('dialog.users', [options], function(){
            callback.apply(self);
          });
        }
      }
docs: Send a request to list users with the given ids.