ContextCalculator docs state it must be thread safe, but use a potentially unsafe example about spongedocs

[A248]

@ST-DDT I am afraid that 07292b8 is not sufficient to make the example thread safe. The code is still vulnerable to race conditions in ways beside the mere use of a HashMap. For example:

if (this.playerArenas.containsKey(uuid)) {
    accumulator.add(IN_ANY_ARENA);
    accumulator.add(new Context(ARENA_KEY, this.playerArenas.get(uuid))); // Possible NPE, Context enforces nonnull value
} else {
    accumulator.add(NOT_ANY_ARENA);
}

[ST-DDT]

Should be fixed now.

[A248]

Awesome