Upstream has released updates that appears to apply and compile correctly.
This update has been tested to ensure that World Conversion still occurs correctly.
Bukkit Changes:
0812ce2c SPIGOT-4397: isChunkGenerated API
CraftBukkit Changes:
4824655c SPIGOT-4398: Upgrade to ASM 6.2.1 for better Java 11 support
eea43870 MC-134115: Fix issues converting tile entities
1a7f2d10 SPIGOT-4397: isChunkGenerated API
40aed54d SPIGOT-4396: Improve vehicle movement
Spigot Changes:
f6a273b1 Rebuild patches
Found some more unsafe operations in DataFixers.
Also replaced quite a few bad uses of Map.containsKey
containsKey is a common newbie mistake that "reads" cleaner, but
results in double the performance cost of all map operations as
containsKey in MOST cases where null values are not used is identical to get() == null
Considering how deep datafixers go in call stacks, with tons of map lookups,
this micro optimization could provide some gains.
Additionally, many of the containsKey/get/put style operations were
also a concurrency risk, resulting in multiple computation/insertions.
Aikar