Custom Field Conditionals

Hi! I hope you can help. I am using More Fields to setup custom fields for posts on a certain category. The first field outputs the image url and the second field outputs the amazon link.

I added a conditional that if a particular custom field is empty, it should output nothing.

My code is below:

// Add Book Image to Books and Excerpts Page
add_action( 'genesis_before_post_content', 'appendBookCover' );
function appendBookCover() { ?>
	<?php $bookcover = get_post_custom_values('book-cover'); ?>
	<?php if (!empty($bookcover) && in_category('9')) {
		echo '<img src="';
		echo meta('book-cover');
		echo '" style="float:left;padding:5px 15px 15px 0;" class="books" />';
    } else {
		echo '';
    } ?>
<?php }

// Add Amazon Button to Books and Excerpts Page
add_action( 'genesis_post_content', 'appendAmazon' );
function appendAmazon() { ?>
	<?php $amazon = get_post_custom_values('amazon-link'); ?>
	<?php if (!empty($amazon) && in_category('9')) {
		echo '<a href="';
		echo meta('amazon-link');
		echo '"><img src="https://dev2.firstplanbcompany.com/demo-think/wp-content/uploads/2012/01/button.gif" style="float:right;clear:both;" class="books" /></a>';
	} else {
		echo '';
    } ?>
<?php }

The code above works great if you haven’t set any value for a field yet. However, if you have already entered a value, saved the post, then later changed your mind and deleted the field value — it no longer works.

It still outputs data as if you have specified a value to the field although you have already emptied it.

What modifications should I do to the code to properly implement this? Thank you. Your help is appreciated.