Updated Upstream (Bukkit/CraftBukkit/Spigot)

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

Please note that this build includes changes to meet upstreams
requirements for nullability annotations. While we aim for a level of
accuracy, these might not be 100% correct, if there are any issues,
please speak to us on discord, or open an issue on the tracker to
discuss.

Bukkit Changes:
9a6a1de3 Remove nullability annotations from enum constructors
3f0591ea SPIGOT-2540: Add nullability annotations to entire Bukkit API

CraftBukkit Changes:
8d8475fc SPIGOT-4666: Force parameter in HumanEntity#sleep
8b1588e2 Fix ExplosionPrimeEvent#setFire not working with EnderCrystals
39a287b7 Don't ignore newlines in PlayerListHeader/Footer

Spigot Changes:
cf694d87 Add nullability annotations

Spigot-API-Patches/SkeletonHorse-Additions.patch

@@ -6,7 +6,7 @@ Subject: [PATCH] SkeletonHorse Additions
 
 diff --git a/src/main/java/com/destroystokyo/paper/event/entity/SkeletonHorseTrapEvent.java b/src/main/java/com/destroystokyo/paper/event/entity/SkeletonHorseTrapEvent.java
 new file mode 100644
-index 00000000..55bae018
+index 000000000..d79dbcd68
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/event/entity/SkeletonHorseTrapEvent.java
 @@ -0,0 +0,0 @@
@@ -16,6 +16,7 @@ index 00000000..55bae018
 +import org.bukkit.event.Cancellable;
 +import org.bukkit.event.HandlerList;
 +import org.bukkit.event.entity.EntityEvent;
++import org.jetbrains.annotations.NotNull;
 +
 +/**
 + * Event called when a player gets close to a skeleton horse and triggers the lightning trap
@@ -24,10 +25,11 @@ index 00000000..55bae018
 +    private static final HandlerList handlers = new HandlerList();
 +    private boolean cancelled;
 +
-+    public SkeletonHorseTrapEvent(SkeletonHorse horse) {
++    public SkeletonHorseTrapEvent(@NotNull SkeletonHorse horse) {
 +        super(horse);
 +    }
 +
++    @NotNull
 +    @Override
 +    public SkeletonHorse getEntity() {
 +        return (SkeletonHorse) super.getEntity();
@@ -43,18 +45,20 @@ index 00000000..55bae018
 +        this.cancelled = cancel;
 +    }
 +
++    @NotNull
 +    @Override
 +    public HandlerList getHandlers() {
 +        return handlers;
 +    }
 +
++    @NotNull
 +    public static HandlerList getHandlerList() {
 +        return handlers;
 +    }
 +}
 +
 diff --git a/src/main/java/org/bukkit/entity/SkeletonHorse.java b/src/main/java/org/bukkit/entity/SkeletonHorse.java
-index b2c6b6a8..ba998346 100644
+index b2c6b6a86..ba9983463 100644
 --- a/src/main/java/org/bukkit/entity/SkeletonHorse.java
 +++ b/src/main/java/org/bukkit/entity/SkeletonHorse.java
 @@ -0,0 +0,0 @@ package org.bukkit.entity;