Strange NullPointerException being encountered, but participating objects are NOT null. This can be verified via the log & code files provided. Basically, I create a new Bossbar. When a player logs in, I add them to this Bossbar. However, on the .addPlayer(Player p) method is when the NullPointer gets thrown.
This makes no sense, as I know for a fact that all participating objects are not null. I also updated to the latest spigot version & latest build tool versions.
I have tested and retested 500 times, but everything points to the add() method, and I know with certainty that the passed values are not null.