Hello,
Thank you so much for contacting us.
Yes, we some small problem in our theme, thank you for your report. We will fix this in next update but as for temporal solution you can find the following code in the file basel/inc/woocommerce.php
$next = wc_get_product( $next->ID );
$prev = wc_get_product( $prev->ID );
and replace with the following
$next = ( ! empty( $next ) ) ? wc_get_product( $next->ID ) : false;
$prev = ( ! empty( $prev ) ) ? wc_get_product( $prev->ID ) : false;
Or you can just ignore this notice until the next update will be released.
Kind regards,
Xtemos