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/EntityRegainHealthEvent-isFastRegen-API.patch

@@ -5,7 +5,7 @@ Subject: [PATCH] EntityRegainHealthEvent isFastRegen API
 
 
 diff --git a/src/main/java/org/bukkit/event/entity/EntityRegainHealthEvent.java b/src/main/java/org/bukkit/event/entity/EntityRegainHealthEvent.java
-index 976b80b7..a5ac3edf 100644
+index 8feb6698..d51d2ec1 100644
 --- a/src/main/java/org/bukkit/event/entity/EntityRegainHealthEvent.java
 +++ b/src/main/java/org/bukkit/event/entity/EntityRegainHealthEvent.java
 @@ -0,0 +0,0 @@ public class EntityRegainHealthEvent extends EntityEvent implements Cancellable
@@ -14,12 +14,12 @@ index 976b80b7..a5ac3edf 100644
      private final RegainReason regainReason;
 +    private final boolean isFastRegen; // Paper
  
-     public EntityRegainHealthEvent(final Entity entity, final double amount, final RegainReason regainReason) {
+     public EntityRegainHealthEvent(@NotNull final Entity entity, final double amount, @NotNull final RegainReason regainReason) {
 +        // Paper start - Forward
 +        this(entity, amount, regainReason, false);
 +    }
 +
-+    public EntityRegainHealthEvent(final Entity entity, final double amount, final RegainReason regainReason, boolean isFastRegen) {
++    public EntityRegainHealthEvent(@NotNull final Entity entity, final double amount, @NotNull final RegainReason regainReason, boolean isFastRegen) {
 +        // Paper end
          super(entity);
          this.amount = amount;