<?php
$wpblog_fetrdimg = wp_get_attachment_url( get_post_thumbnail_id($post->ID) );
?>
<div class="wpblog-featured-image"
<?php if( $wpblog_fetrdimg ) : ?>
style="wpblog-featured-background-image: url(<?php echo $wpblog_fetrdimg; ?>);"
<?php endif; ?>
>
</div>
See if this works.