What does the law say about Cameron Green's controversial catch to dismiss Shubman Gill?

Australia all-rounder Cameron Green took a low catch to dismiss India opener Shubman Gill in WTC final. Replays seemingly showed the ball touching the ground. As per law, if the fielder's fingers are underneath the ball and he has complete control of ball and his movement, the catch will prevail even if a part of ball is touching the grass.