SPIGOT-2540: Add nullability annotations to entire Bukkit API

By: Darkyenus <darkyenus@gmail.com>

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

@@ -1,6 +1,7 @@
 package org.bukkit.entity;
 
 import org.bukkit.Location;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * Represents a Primed TNT.
@@ -36,5 +37,6 @@ public interface TNTPrimed extends Explosive {
      *
      * @return the source of this primed TNT
      */
+    @Nullable
     public Entity getSource();
 }