Create WordPress Gallery from BuddyForms File Form Element to use in a ShortCode

buddyforms_custom_gallery_shortcode.php

<?php
// Register the new Shortcode
add_shortcode( 'my_bf_gallery_shortcode' , 'my_custom_gallery_shortcode' );

// ShortCode function:
function my_custom_gallery_shortcode($attr){
    global $post, $buddyforms;

    extract(shortcode_atts(array(
        'form_element_slug' => '',
    ), $attr));
  
    if(is_admin())
        return;
        
    // get the form element (custom field) values
    $gallery = get_post_meta($post->ID, $form_element_slug, true);

    if(!$gallery)
        return;

    // Create a "," seperated string from the attachement ids
    $gallery = implode(',', $gallery);
  
    // create the WP Gallery Shortcode and return it 
    $gallery_shortcode = '[gallery ids="'. $gallery .'"]';
    return apply_filters( 'the_content', $gallery_shortcode );
}