Populate Post Title with ACF field value

functions.php

 //Auto add and update Title field:
   function my_post_title_updater( $post_id ) {

     $my_post = array();
     $my_post['ID'] = $post_id;

 // custom post type

     if ( get_post_type() == 'case_study' ) {
       $my_post['post_title'] = get_field('case_study_title');
     }

     // Update the post into the database
     wp_update_post( $my_post );

   }

   // run after ACF saves the $_POST['fields'] data
   add_action('acf/save_post', 'my_post_title_updater', 20);
 //END Auto add and update Title field: