SQL Query Tax Rate of purchase Order At line level

Dear All,

I'm currently encountering an issue while attempting to query the tax of a purchase order at the line level. Upon inspection, I've noticed that the fields "tax_name" and "tax_code" are both null in the "po_lines_all" table.

I am certain that there are values present in the SaaS for this particular purchase order line. 

Can anyone tell me why these two values are null, and if these fields indeed remain empty, how can I retrieve the tax at the line level?

Thank you in advance,