Using ‘excerpt’ because no post ‘subtitle’… not optimal

Is there an easy way I’m missing to add a subtitle to a post? The two plug-ins available are broken.

Using excerpt works fine except if there is no custom text in the excerpt field it grabs the content from the post:

<div><?php echo get_the_excerpt(); ?></div>

I guess there’s no way to see if it’s null because it takes the post content next?

Thanks for your help