api: mark getItemDefinition as nonnull

runelite-client/src/main/java/net/runelite/client/game/ItemManager.java

@@ -38,6 +38,7 @@ import java.util.Map;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
+import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import javax.inject.Inject;
 import javax.inject.Singleton;
@@ -363,6 +364,7 @@ public class ItemManager
 	 * @param itemId item id
 	 * @return item composition
 	 */
+	@Nonnull
 	public ItemComposition getItemComposition(int itemId)
 	{
 		assert client.isClientThread() : "getItemComposition must be called on client thread";