Only output content if there are rows
<?php
$rows = get_field( 'sermon_series_media' ); // Get all the rows
if ($rows) {
$first_row_date = $rows[0]['sermon_date']; // Get the first row
$last_row = end( $rows );
$last_row_date = $last_row['sermon_date']; // Get the sub field value
if( $last_row_date ) :
?>
<div class="archive-sermon-date-range">
<?php
echo last_row_date;
if( $last_row_date != $first_row_date ) :
?> - <?php echo $first_row_date;
php endif;
?>
</div>
<?php
endif;
} // end if $rows
