I cannot reproduce that on our end. When I create a tax rule without a tax category, nothing is displayed for that tax rule in the tax category column on the tax rules listing.
The only explanation I would see is that you have in the table hikashop_category a category with nothing in the column category_namekey which should not happen normally.
You could try to change the line
Code:
$query = ' FROM '.hikashop::table('taxation').' AS a LEFT JOIN '.hikashop::table('tax').' AS b ON a.tax_namekey=b.tax_namekey LEFT JOIN '.hikashop::table('category').' AS c ON a.category_namekey=c.category_namekey LEFT JOIN '.hikashop::table('zone').' AS d ON a.zone_namekey=d.zone_namekey'.$filters.$order;
to
Code:
$query = ' FROM '.hikashop::table('taxation').' AS a LEFT JOIN '.hikashop::table('tax').' AS b ON a.tax_namekey=b.tax_namekey LEFT JOIN '.hikashop::table('category').' AS c ON a.category_namekey=c.category_namekey AND a.category_namekey!=\'\' AND c.category_type=\'tax\' LEFT JOIN '.hikashop::table('zone').' AS d ON a.zone_namekey=d.zone_namekey AND a.zone_namekey!=\'\''.$filters.$order;
in the file administrator/components/com_hikashop/views/taxation/view.html.php
