Next & Prev Post

I am building a custom theme and i’m using the post thumbnail function to show next and previous posts in my sidebar.

Here is the code i’m using

<div class="previmg">

<?php if(get_adjacent_post(false, '', true)) : // check for the existance of a prev post ?>

                            <?php $post_thumbnail = get_post_meta($post->ID, 'post_thumbnail', true);
                            if ($post_thumbnail) {
                            ?>
                            <a href="<?php previous_post_link(); ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php echo $post_thumbnail; ?></a>

                            <?php } else { ?>

                            <?php $prevPost = get_previous_post(); $prevthumbnail = get_the_post_thumbnail($prevPost->ID, array(66,66) ); previous_post_link('%link',''.$prevthumbnail.'', TRUE); ?>

                            <?php } ?>

                            <?php else : // if no prev post ?>

                            <img src="<?php bloginfo('template_url'); ?>/images/empty.jpg"/>

                            <?php endif; // end of the prev post check ?>

</div>

<div class="nextimg">  

								<?php if(get_adjacent_post(false, '', false)) : // check for the existance of a next post ?>

                                <?php $post_thumbnail = get_post_meta($post->ID, 'post_thumbnail', true);
                                if ($post_thumbnail) {
                                ?>
                                <a href="<?php next_post_link(); ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php echo $post_thumbnail; ?></a>

                                <?php } else { ?>

                                <?php $nextPost = get_next_post(true); $nextthumbnail = get_the_post_thumbnail($nextPost->ID, array(66,66) ); next_post_link('%link',''.$nextthumbnail.'', TRUE); ?>

                                <?php } ?>

                                <?php else : // if no prev post ?>

                                <img src="<?php bloginfo('template_url'); ?>/images/empty.jpg"/>

                                <?php endif; // end of the prev post check ?>

                            </div>

I’m having a issue when I get the the forth post. It seems to just show an empty image which I dont want.

Any ideas on how to fix it?

Thanks

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