This commit: https://hub.spigotmc.org/stash/projects/SPIGOT/repos/bukkit/commits/67d908a9830c71267ee740f5bddd728ce9c64cc7#src/main/java/org/bukkit/entity/EntityType.java
removed the "TIPPED_ARROW" entity type, and changed ARROW to be a reference to TippedArrow. They are still separate types internally, and should still both be available. These are indeed now separate types internally, however the spawning logic should be updated to reflect that an "Arrow" is normally just an arrow, not a tipped arrow (until a tip is added).
The world#spawnArrow method will allow correctly spawning them separately using Arrow.class and TippedArrow.class ... the world#spawnEntity method, when fed EntityType.ARROW, will spawn an arrow that contains an invalid tip. When picked up, such arrows will display as "Arrow of Splashing" (a tipped arrow item with no potion effect to apply). They visible give off a water-blue potion particle.
The correct behavior of course should be not having any tip until/unless a potion tip is set.