Sales tax group mandatory in the PO invoice charge line.

When we adding the charges in the purchase order invoice and system allow to save the charge code and post the invoice with out sales tax group. As per the Italian law, sales tax group is mandatory field for the charges. System should not allow the charge code to save or post the invoice without sales tax group in the charges. Here the article of law by Italian Ministry of Economy: https://def.finanze.it/DocTribFrontend/getAttoNormativoDetail.do?ACTION=getArticolo&id={75A4827C-3766-4ECC-9C45-00C8D6CDC552}&codiceOrdinamento=200001200000000&articolo=Articolo%2012