protected function getColumns($controller)
    {
        // If user has defined columns, use them
        if ($this->columns) {
            return $this->columns;
        }

        // Read columns from the controller
        $columns = $controller->columns();

        // If showing in sidebar, only show the first column
        // http://stackoverflow.com/a/1028677/59160
        if ($this->layout == 'sidebar') {
            $val = reset($columns); // Making sure this gets called before `key()`
            return [key($columns) => $val];

        // Otherwise, just return all columns
        }

        return $columns;
    }