SPIGOT-2540: Add nullability annotations to entire Bukkit API

By: Darkyenus <darkyenus@gmail.com>

paper-api/src/main/java/org/bukkit/block/Jukebox.java

@@ -2,6 +2,8 @@ package org.bukkit.block;
 
 import org.bukkit.Material;
 import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * Represents a captured state of a jukebox.
@@ -13,6 +15,7 @@ public interface Jukebox extends BlockState {
      *
      * @return The record Material, or AIR if none is inserted
      */
+    @NotNull
     public Material getPlaying();
 
     /**
@@ -20,13 +23,14 @@ public interface Jukebox extends BlockState {
      *
      * @param record The record Material, or null/AIR to stop playing
      */
-    public void setPlaying(Material record);
+    public void setPlaying(@Nullable Material record);
 
     /**
      * Gets the record item inserted into the jukebox.
      *
      * @return a copy of the inserted record, or an air stack if none
      */
+    @NotNull
     public ItemStack getRecord();
 
     /**
@@ -34,7 +38,7 @@ public interface Jukebox extends BlockState {
      *
      * @param record the record to insert or null/AIR to empty
      */
-    public void setRecord(ItemStack record);
+    public void setRecord(@Nullable ItemStack record);
 
     /**
      * Checks if the jukebox is playing a record.