Bukkit

When I start the server it always says this in the command prompt:

1:28:38 PM [WARNING] [HungerPlusPlus] Plugin HungerPlusPlus v0.4a generated an exception while executing task 6
1:28:38 PM java.lang.NoSuchMethodError: org.bukkit.Server.getOnlinePlayers()[Lorg/bukkit/entity/Player;
1:28:38 PM at com.gmail.twilight13.HungerPlusPlus.Metrics.postPlugin(Metrics.java:357) ~[?:?]
1:28:38 PM at com.gmail.twilight13.HungerPlusPlus.Metrics.access$4(Metrics.java:350) ~[?:?]
1:28:38 PM at com.gmail.twilight13.HungerPlusPlus.Metrics$1.run(Metrics.java:245) ~[?:?]
1:28:38 PM at org.bukkit.craftbukkit.v1_11_R1.scheduler.CraftTask.run(CraftTask.java:71) ~[spigot.jar:git-Spigot-7d78b81-0fb3f8b]
1:28:38 PM at org.bukkit.craftbukkit.v1_11_R1.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:52) [spigot.jar:git-Spigot-7d78b81-0fb3f8b]
1:28:38 PM at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [?:1.8.0_111]
1:28:38 PM at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [?:1.8.0_111]
1:28:38 PM at java.lang.Thread.run(Unknown Source) [?:1.8.0_111]

Not sure what it means, P.S I'm not anywhere near good in technology. It doesn't seem like anything happens in game.