Upstream has released updates that appears to apply and compile correctly.
This update has not been tested by PaperMC and as with ANY update, please do your own testing
Bukkit Changes:
122289ff Add FaceAttachable interface to handle Grindstone facing in common with Switches
a6db750e SPIGOT-5647: ZombieVillager entity should have getVillagerType()
CraftBukkit Changes:
bbe3d58e SPIGOT-5650: Lectern.setPage(int) causes a NullPointerException
3075579f Add FaceAttachable interface to handle Grindstone facing in common with Switches
95bd4238 SPIGOT-5647: ZombieVillager entity should have getVillagerType()
4d975ac3 SPIGOT-5617: setBlockData does not work when NotPlayEvent is called by redstone current
Previous solution could still block network thread (while addPending is executing). This window is small, but removing it completely is better. This should probably also speed up concurrent adds, because no locking will be performed anymore.
The only possible downside is that adding elements one by one to synchronized list might be slower (But it's done while already locked, so maybe jvm will avoid additional locking?),
