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/Access-items-by-EquipmentSlot.patch

@@ -5,12 +5,12 @@ Subject: [PATCH] Access items by EquipmentSlot
 
 
 diff --git a/src/main/java/org/bukkit/inventory/PlayerInventory.java b/src/main/java/org/bukkit/inventory/PlayerInventory.java
-index fc5772e8..d56f6e00 100644
+index ef55b1463..eb71f01e4 100644
 --- a/src/main/java/org/bukkit/inventory/PlayerInventory.java
 +++ b/src/main/java/org/bukkit/inventory/PlayerInventory.java
 @@ -0,0 +0,0 @@ public interface PlayerInventory extends Inventory {
-     public void setHeldItemSlot(int slot);
  
+     @Nullable
      public HumanEntity getHolder();
 +
 +    // Paper start
@@ -20,7 +20,8 @@ index fc5772e8..d56f6e00 100644
 +     * @param slot The slot
 +     * @return The item stack in the slot
 +     */
-+    ItemStack getItem(EquipmentSlot slot);
++    @Nullable
++    ItemStack getItem(@NotNull EquipmentSlot slot);
 +
 +    /**
 +     * Sets the {@link ItemStack} at the given {@link EquipmentSlot}.
@@ -28,7 +29,7 @@ index fc5772e8..d56f6e00 100644
 +     * @param slot The slot for the stack
 +     * @param stack The item stack to set
 +     */
-+    void setItem(EquipmentSlot slot, ItemStack stack);
++    void setItem(@NotNull EquipmentSlot slot, @Nullable ItemStack stack);
 +    // Paper end
  }
 --