SPIGOT-2540: Add nullability annotations to entire Bukkit API

By: Darkyenus <darkyenus@gmail.com>

paper-api/src/main/java/org/bukkit/entity/EnderDragonPart.java

@@ -1,8 +1,11 @@
 package org.bukkit.entity;
 
+import org.jetbrains.annotations.NotNull;
+
 /**
  * Represents an ender dragon part
  */
 public interface EnderDragonPart extends ComplexEntityPart, Damageable {
+    @NotNull
     public EnderDragon getParent();
 }