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
CraftBukkit Changes:
eb2e6578 SPIGOT-5116: Fix concurrent modification exception inside ChunkMapDistance
989f9b3d SPIGOT-4849: Fix server crash when accessing chunks during chunk load/unload/populate events
f554183c SPIGOT-5171: Don't fire PlayerTeleportEvent if not actually moving
2349feb8 SPIGOT-5163: Cancelling PlayerBucketFillEvent visually removes the targeted block
Spigot Changes:
9a643a6a Remove DataWatcher Locking
This makes it easier for downstream projects (forks) to replace the
version fetching system with their own. It is as simple as implementing
an interface and overriding the default implementation of
org.bukkit.UnsafeValues#getVersionFetcher()
It also makes it easier for us to organize things like the version
history feature.
Lastly I have updated the paper implementation to check against the site
API rather than against jenkins.
We were missing a synchronize on a get if cached method, however
it appears that using a ConcurrentHashMap is a better solution
so readers can avoid locking if they just want a cached value.
Existing synchronization for writers remains untouched, the
ConcurrentHashMap is just so readers can safely read without
synchronization
Shane Freeder
Zach Brown
Spottedleaf