Set Empty Value to Child Table Field with Link Type Data (Item Tax Template on Child Table)

Hi, i made custom on Items doctype to set Item Tax per item like this.

Item 003 set PPN as Selling Transaction

Server Side
Set condition if type of transacation is Selling or Buying and get Tax Template

Script Side

On Purchase Order Document = Buying Transaction i call item 003 that i set sellling item tax but on items at field Item Tax Template = PPN (which is Selling Tax) that i want is Item Tax Template = Empty because is not Selling transaction

Thanks & Regards.

Hi, is there solutions to my case? or must be fill in array?