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:
a8887389 Make AreaEffectCloudApplyEvent cancellable
CraftBukkit Changes:
a2dd0e30 SPIGOT-4615: Missing target event for withers
b26fb374 Update outdated spigot link
2b1940ae Make AreaEffectCloudApplyEvent cancellable
13f722fe43