Check if ACF fields exists

gistfile1.php

		<?php elseif ( has_post_thumbnail() ) :
			$featured_image_link = ( get_field( 'featured_image_links_to' ) );
			if ( $featured_image_link ) {
				echo '<a href="'.get_permalink($post_object->ID) .'">';
					if ( has_post_thumbnail()) {  the_post_thumbnail( 'hero-image-medium', array( 'class' => 'large fx' ) ); } 
				echo '</a>';	  
			} else {
				the_post_thumbnail( 'hero-image-medium', array( 'class' => 'large fx' ) );
			};
		endif; ?>