Hi @iamjustoneman
A simple if statement will work like so:
<?php if(get_field('clients')): ?>
<div class="col clients boxed">
<h3>Clients</h3>
<ul id="client-list">
<?php while(has_sub_field('clients')): ?>
<li>
<?php if( get_sub_field('case_study_page'); ): ?>
<a href="<?php the_sub_field('case_study_page'); ?>">
<?php the_sub_field('client_name'); ?>
</a>
<?php else: ?>
<?php the_sub_field('client_name'); ?>
<?php endif; ?>
</li>
<?php endwhile; ?>
</ul>
</div>
<?php endif; ?>