Mark PlayerInventory#getItem as nullable

Spigot-API-Patches/Fix-upstream-javadoc-warnings-and-errors.patch

@@ -63,3 +63,16 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      public Location getTo() {
          return to;
      }
+diff --git a/src/main/java/org/bukkit/inventory/PlayerInventory.java b/src/main/java/org/bukkit/inventory/PlayerInventory.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 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 {
+      *
+      * @return the ItemStack in the given slot
+      */
+-    @NotNull
++    @Nullable
+     public ItemStack getItem(@NotNull EquipmentSlot slot);
+ 
+     /**