Research and read the case of PHILIPPINE NATIONAL OIL COMPANY, ET AL. VS. KEPPEL PHILIPPINES HOLDING, INC.; G.R. NO. 202050; JULY 25, 2016. Here's the link: https://www.chanrobles.com/cralaw/2016julydecisions.php?id=648

After reading, make a brief and concise discussion paper discussing the material principles and rules on the Law on Sales as can be inferred from the said case.