Add the unnecessary annotation

cmon, that wasn't even API.

i've updated my IDE to now not skip tests :(

Spigot-API-Patches/0004-Timings-v2.patch

@@ -1,4 +1,4 @@
-From 5c0ebe352e7ae47be75b657d8ff45ed1751a9dd0 Mon Sep 17 00:00:00 2001
+From 24d273e696fc58bf34246300ee6199f5dbb1f7ba Mon Sep 17 00:00:00 2001
 From: Aikar <aikar@aikar.co>
 Date: Mon, 29 Feb 2016 18:48:17 -0600
 Subject: [PATCH] Timings v2
@@ -475,10 +475,10 @@ index 000000000..a5d13a1e4
 +}
 diff --git a/src/main/java/co/aikar/timings/TimingHandler.java b/src/main/java/co/aikar/timings/TimingHandler.java
 new file mode 100644
-index 000000000..4e6994098
+index 000000000..2a727994a
 --- /dev/null
 +++ b/src/main/java/co/aikar/timings/TimingHandler.java
-@@ -0,0 +1,201 @@
+@@ -0,0 +1,202 @@
 +/*
 + * This file is licensed under the MIT License (MIT).
 + *
@@ -515,6 +515,7 @@ index 000000000..4e6994098
 +
 +import org.bukkit.Bukkit;
 +import org.jetbrains.annotations.NotNull;
++import org.jetbrains.annotations.Nullable;
 +
 +class TimingHandler implements Timing {
 +
@@ -602,7 +603,7 @@ index 000000000..4e6994098
 +
 +    }
 +
-+    void addDiff(long diff, TimingHandler parent) {
++    void addDiff(long diff, @Nullable TimingHandler parent) {
 +        if (parent != null) {
 +            parent.children.get(id).add(diff);
 +        }