Bukkit

What steps will reproduce the problem?
1.using a sign
2.setting a warp
3.running server with plugin installed

What is the expected output? What do you see instead?
everything works as needed but produces masses of error messages spamming my console.

What version of the product are you using?
5.2 1.7.2

Do you have an error log of what happened?
[03:14:36 WARN]: Exception in thread "pool-3-thread-6"
[03:14:36 WARN]: org.apache.commons.lang.UnhandledException: Plugin WarpSigns v5.2 generated an exception while executing task 6
        at org.bukkit.craftbukkit.v1_9_R1.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NoSuchMethodError: org.bukkit.Server.getOnlinePlayers()[Lorg/bukkit/entity/Player;
        at com.huskehhh.warpsigns.metrics.Metrics.postPlugin(Metrics.java:364)
        at com.huskehhh.warpsigns.metrics.Metrics.access$500(Metrics.java:68)
        at com.huskehhh.warpsigns.metrics.Metrics$1.run(Metrics.java:256)
        at org.bukkit.craftbukkit.v1_9_R1.scheduler.CraftTask.run(CraftTask.java:53)
        at org.bukkit.craftbukkit.v1_9_R1.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
        ... 3 more

Please provide any additional information below.
all works right but provides errors spamming my console just worried may cause crashes etc.