The contents slot for the /item command does not function with thrown splash/lingering potions

The bug

The contents slot is supposed to provide access to the item stack of any entity that logically contains one. It already works for dropped items, item frames, item displays, and, since MC-270119 was fixed, arrows, tridents, and fireballs.

However, it does not work for thrown splash or lingering potions.

How to reproduce

1. Throw a splash potion into a cobweb

2. Before it lands, run this command:

   /item replace entity @n[type=splash_potion] contents with apple

Expected result

The splash potion should look like an apple

Observed result

Command fails: “The target does not have slot contents”