acf true false field default value

CSS
<?php 
    $show_sidebar = get_post_meta($post->ID, 'show_sidebar', true);
    if($show_sidebar === '' || $show_sidebar === '1'): ?>
<div id="sidebar">
<?php if ( !function_exists('dynamic_sidebar') || !dynamic_sidebar('Sidebar') ) : ?><?php endif; ?>
</div>
<?php endif; ?>
Source