[PRESTASHOP] fix Undefined offset error

Hi, We're experiencing this error on our Prestashop (1.6) on top of the homepage when you go to the site. Notice: Undefined offset: 6 in /var/www/vhosts/ourdomain/classes/tax/[login to view URL] on line 124 If you then put an article in the cart you get this error: Impossible to add the product to the cart. textStatus: 'parsererror' errorThrown: 'SyntaxError: Unexpected token < in JSON at position 0' responseText: Notice: Undefined offset: 6 in /var/www/vhosts/[login to view URL] on line 124 Notice: Undefined offset: 6 in /var/www/vhosts/ourdomain/classes/tax/[login to view URL] on line 124 {"products":[{"id":2222,"link":"http:\/\/OURDOMAIN\/[login to view URL]","quantity":1,"image":"http:\/\/OURDOMAIN\/img\/p\/[login to view URL]","image_cart":"http:\/\/OURDOMAIN\/img\/p\/[login to view URL]","priceByLine":"117,36\u20ac","name":"Lego 9333 voertuigenset","price":"117,36\u20ac","price_float":96.991736,"idCombination":0,"idAddressDelivery":0,"is_gift":false,"hasAttributes":false,"hasCustomizedDatas":false,"customizedDatas":[]}],"discounts":[],"shippingCost":"0,00\u20ac","shippingCostFloat":0,"taxCost":"20,37\u20ac","wrappingCost":"0,00\u20ac","nbTotalProducts":1,"total":"117,36\u20ac","productTotal":"117,36\u20ac","freeShipping":"0,00\u20ac","freeShippingFloat":0,"hasError":false,"crossSelling":""}