SPIGOT-2540: Add nullability annotations to entire Bukkit API

By: Darkyenus <darkyenus@gmail.com>

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

@@ -3,6 +3,7 @@ package org.bukkit.loot;
 import org.bukkit.Bukkit;
 import org.bukkit.Keyed;
 import org.bukkit.NamespacedKey;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * This enum holds a list of all known {@link LootTable}s offered by Mojang.
@@ -118,10 +119,11 @@ public enum LootTables implements Keyed {
 
     private final String location;
 
-    private LootTables(String location) {
+    private LootTables(@NotNull String location) {
         this.location = location;
     }
 
+    @NotNull
     @Override
     public NamespacedKey getKey() {
         return NamespacedKey.minecraft(location);
@@ -133,6 +135,7 @@ public enum LootTables implements Keyed {
      *
      * @return the associated LootTable
      */
+    @NotNull
     public LootTable getLootTable() {
         return Bukkit.getLootTable(getKey());
     }