I used your code, Tim and am getting this PHP error:
Error while parsing PHP: syntax error, unexpected 'else' (T_ELSE)
my code:
<?php if ( get_field( 'btn_show' ) ); ?>
<p class="text-center"><a class="btn" href="<?php the_sub_field('btn_url'); ?>"><?php the_sub_field('btn_text'); ?></a></p>
<?php else: // field_name returned false ?>
<?php endif; // field_name ?>