Get Terms issue

I am getting the error: Notice: Undefined offset: 0 in ../wp-includes/query.php on line 2258. The code giving me that error is below:

<?php $sermon_series_terms = get_the_terms( $post->ID, 'sermon_series' );
    if ( $sermon_series_terms )
	$sermon_series_term_slugs = wp_list_pluck( $sermon_series_terms, 'slug' );
		$args = array(
		'post_type' => 'sermons',
		'order' => 'ASC',
		'tax_query' => array(
		array(
		'taxonomy' => 'sermon_series',
		'field' => 'slug',
		'terms' => $sermon_series_term_slugs
		)
		)
	);?>
	<?php $my_query = new WP_Query(); $my_query->query($args); ?>
	<?php while ($my_query->have_posts()) : $my_query->the_post(); ?>
	<li><a href="<?php the_permalink(); ?>" style="font-style:normal;"><?php the_title(); ?></a></li>
	<?php wp_reset_postdata(); endwhile; ?>

Basically I am trying to get all of the post titles within the current posts (on a custom post types single.php) custom taxonomy in a list. You can view the page at http://mrp.trbc.org/trbc2013/sermons/living-in-the-margin/.