Fixed the NullPointerException caused by AreaEffectCloud.

Also, any Creeper related Kill death messages stopped working in 1.14, because a dead entity is no longer searchable through the list of entities in the world. Because of this, no Creeper message or any other message where the mob had already died before the player would work (instead, they would display the death message as if their death weren't caused by a mob). For this version, I included a small patch that hardcodes the Creeper FallExplosionKill message if a Creeper happens to kill the player by blowing them off a cliff or similar. This however may not work well with addons, as despite being FallExplosionKill, the death event has no damager. I'm looking for a better solution.