Add missing NotNull annotation for getChunksAtAsync cb param

patches/api/0139-Async-Chunks-API.patch

@@ -8,7 +8,7 @@ Adds API's to load or generate chunks asynchronously.
 Also adds utility methods to Entity to teleport asynchronously.
 
 diff --git a/src/main/java/org/bukkit/World.java b/src/main/java/org/bukkit/World.java
-index ba9ab1d46effe1e6c08cebddb8b856e2b294d7cb..f314f8bc5c437c5703c1e093278d9046903ff2c8 100644
+index ba9ab1d46effe1e6c08cebddb8b856e2b294d7cb..1161c286aaaaad761c80ca97c25fd166365bb044 100644
 --- a/src/main/java/org/bukkit/World.java
 +++ b/src/main/java/org/bukkit/World.java
 @@ -977,6 +977,509 @@ public interface World extends RegionAccessor, WorldInfo, PluginMessageRecipient
@@ -203,7 +203,7 @@ index ba9ab1d46effe1e6c08cebddb8b856e2b294d7cb..f314f8bc5c437c5703c1e093278d9046
 +     * @see Chunk
 +     */
 +    void getChunksAtAsync(final int minX, final int minZ, final int maxX, final int maxZ, final boolean urgent,
-+                          final Runnable cb);
++                          final @NotNull Runnable cb);
 +
 +    /**
 +     * Requests a {@link Chunk} to be loaded at the given {@link Location}