Output selected user

Hi there,

As part of my form, they can select a user. I want to output the display name of the selected user. But can't see where its going wrong! Am I using the correct helper function?

add_shortcode("academic_get_display_name", function (){
	global $post;
	$bbb_post_type = get_post_type($post->ID);
	if('research' === $bbb_post_type){
		$bbb_academic_field = rwmb_meta( 'academicinterview_transfer_author_to_academic','',$post->ID);
		if ($bbb_academic_field){
		$bbb_academic_name = get_userdata($bbb_academic_field)->display_name;

		return $bbb_academic_name;
		}}});