SPIGOT-2540: Add nullability annotations to entire Bukkit API

By: Darkyenus <darkyenus@gmail.com>

paper-api/src/main/java/org/bukkit/loot/Lootable.java

@@ -1,5 +1,7 @@
 package org.bukkit.loot;
 
+import org.jetbrains.annotations.Nullable;
+
 /**
  * Represents a {@link org.bukkit.block.Container} or a
  * {@link org.bukkit.entity.Mob} that can have a loot table.
@@ -20,7 +22,7 @@ public interface Lootable {
      * @param table the Loot Table this {@link org.bukkit.block.Container} or
      * {@link org.bukkit.entity.Mob} will have.
      */
-    void setLootTable(LootTable table);
+    void setLootTable(@Nullable LootTable table);
 
     /**
      * Gets the Loot Table attached to this block or entity.
@@ -31,6 +33,7 @@ public interface Lootable {
      *
      * @return the Loot Table attached to this block or entity.
      */
+    @Nullable
     LootTable getLootTable();
 
     /**