Errors in theme re. Featured Content

Hi, had these errors show up. Not sure what's happening here: Fatal error: Uncaught Error: [] operator not supported for strings in /app/public/wp-content/themes/rock-star/inc/featured-content.php:45 Stack trace: #0 /app/public/wp-includes/class-wp-hook.php(286): rock_star_featured_content_display('') #1 /app/public/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters('', Array) #2 /app/public/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #3 /app/public/wp-content/themes/rock-star/footer.php(34): do_action('rock_star_foote...') #4 /app/public/wp-includes/template.php(688): require_once('/app/public/wp-...') #5 /app/public/wp-includes/template.php(647): load_template('/app/public/wp-...', true) #6 /app/public/wp-includes/general-template.php(76): locate_template(Array, true) #7 /app/public/wp-content/themes/rock-star/page.php(34): get_footer() #8 /app/public/wp-includes/template-loader.php(74): include('/app/public/wp-...') #9 /app/public/wp-blog-header.php(19): require_once('/app/public/wp-...') #10 /app/public/index.php(17): require('/app/public/wp-...') #11 {main} in /app/public/wp-content/themes/rock-star/inc/featured-content.php on line 45