public function preFill($contentTypes = [])
    {
        if (empty($contentTypes)) {
            $contentTypes = $this->app['config']->get('contenttypes');
            $contentTypeNames = array_keys($contentTypes);
        } else {
            $contentTypeNames = (array) $contentTypes;
        }

        /** @var \Bolt\Storage\Database\Prefill\Builder $builder */
        $builder = $this->app['prefill.builder'];
        $results = $builder->build($contentTypeNames, 5);

        $output = '';
        foreach ($results->get('created') as $contentTypeName => $titles) {
            foreach ($titles as $title) {
                $output .= Trans::__(
                    "Added to <tt>%key%</tt> '%title%'",
                    ['%key%' => $contentTypeName, '%title%' => $title['title']]
                );
                $output .= "<br>\n";
            }
        }
        foreach ($results->get('warnings') as $warnings) {
            $output .= $warnings;
        }
        foreach ($results->get('errors') as $errors) {
            $output .= $errors;
        }

        return $output;
    }