SPIGOT-2540: Add nullability annotations to entire Bukkit API

By: Darkyenus <darkyenus@gmail.com>

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

@@ -2,6 +2,8 @@ package org.bukkit.entity;
 
 import org.bukkit.block.data.BlockData;
 import org.bukkit.material.MaterialData;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * Represents an Enderman.
@@ -13,6 +15,7 @@ public interface Enderman extends Monster {
      *
      * @return MaterialData containing the id and data of the block
      */
+    @NotNull
     public MaterialData getCarriedMaterial();
 
     /**
@@ -20,13 +23,14 @@ public interface Enderman extends Monster {
      *
      * @param material data to set the carried block to
      */
-    public void setCarriedMaterial(MaterialData material);
+    public void setCarriedMaterial(@NotNull MaterialData material);
 
     /**
      * Gets the data of the block that the Enderman is carrying.
      *
      * @return BlockData containing the carried block, or null if none
      */
+    @Nullable
     public BlockData getCarriedBlock();
 
     /**
@@ -34,5 +38,5 @@ public interface Enderman extends Monster {
      *
      * @param blockData data to set the carried block to, or null to remove
      */
-    public void setCarriedBlock(BlockData blockData);
+    public void setCarriedBlock(@Nullable BlockData blockData);
 }