add the if condition to check whether array is empty or not like
if (is_array($posts)){
foreach( $posts as $post ) {
// Ignore the topic if included.
if ( bbp_get_reply_post_type() == $post->post_type ) {
$in_reply_to = get_post_meta( $post->ID, ‘_ucc_btr_in_reply_to’, true );
if ( empty( $in_reply_to ) || ( bbp_get_reply_topic_id( $post->ID ) == $in_reply_to ) )
$in_reply_to = 0;
$post->in_reply_to = $in_reply_to;
$replies[] = $post;
} elseif ( bbp_get_topic_post_type() == $post->post_type ) {
delete_post_meta( $post->ID, ‘_ucc_btr_in_reply_to’ );
}
}}