Upstream has released updates that appear 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:
79e39671 SPIGOT-7034: Add methods for set/get instrument in Goat Horn
CraftBukkit Changes:
4768df736 SPIGOT-7034: Add methods for set/get instrument in Goat Horn
941d7e954 SPIGOT-7225: FireworkMeta#getPower() can throw a NullPointerException for items with no power set
