SPIGOT-2540: Add nullability annotations to entire Bukkit API

By: Darkyenus <darkyenus@gmail.com>

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

@@ -1,5 +1,8 @@
 package org.bukkit.entity;
 
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.Nullable;
+
 /**
  * Represents a Zombie.
  */
@@ -33,6 +36,7 @@ public interface Zombie extends Monster {
      * @deprecated must spawn {@link ZombieVillager}.
      */
     @Deprecated
+    @Contract("_ -> fail")
     public void setVillager(boolean flag);
 
     /**
@@ -40,6 +44,7 @@ public interface Zombie extends Monster {
      * @see ZombieVillager#getVillagerProfession()
      */
     @Deprecated
+    @Contract("_ -> fail")
     public void setVillagerProfession(Villager.Profession profession);
 
     /**
@@ -47,6 +52,8 @@ public interface Zombie extends Monster {
      * @see ZombieVillager#getVillagerProfession()
      */
     @Deprecated
+    @Nullable
+    @Contract("-> null")
     public Villager.Profession getVillagerProfession();
 
     /**