Initialise ping array on startup. The code to decide when to regenerate the array is a bit iffy (Mojang!), as it relies on System.nanoTime() which is not an absolute time source.

CraftBukkit-Patches/0102-Fix-Ping-Player-Sample.patch

@@ -1,22 +1,22 @@
-From d8be3082b4cc82d525e1152efc58bced681890b1 Mon Sep 17 00:00:00 2001
+From 331f61fc74453d744df31d52edf5c9b804fb9597 Mon Sep 17 00:00:00 2001
 From: md_5 <git@md-5.net>
 Date: Sun, 26 Jan 2014 12:13:31 +1100
 Subject: [PATCH] Fix Ping Player Sample
 
 
 diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
-index a549a95..e967d17 100644
+index 022e032..9c602b4 100644
 --- a/src/main/java/net/minecraft/server/MinecraftServer.java
 +++ b/src/main/java/net/minecraft/server/MinecraftServer.java
 @@ -105,6 +105,7 @@ public abstract class MinecraftServer implements ICommandListener, Runnable, IMo
      private static final int TPS = 20;
      private static final int TICK_TIME = 1000000000 / TPS;
      public final double[] recentTps = new double[ 3 ];
-+    public EntityPlayer[] pingPlayers;
++    public EntityPlayer[] pingPlayers = new EntityPlayer[ 0 ];
      // Spigot end
  
      public MinecraftServer(OptionSet options, Proxy proxy) { // CraftBukkit - signature file -> OptionSet
-@@ -560,15 +561,23 @@ public abstract class MinecraftServer implements ICommandListener, Runnable, IMo
+@@ -561,15 +562,23 @@ public abstract class MinecraftServer implements ICommandListener, Runnable, IMo
          if (i - this.T >= 5000000000L) {
              this.T = i;
              this.p.setPlayerSample(new ServerPingPlayerSample(this.C(), this.B()));