Signs console error log

[03:02:53 WARN]: Exception in thread "Craft Scheduler Thread - 9"
[03:02:53 WARN]: org.apache.commons.lang.UnhandledException: Plugin Signs v1.8 generated an exception while executing task 77
        at org.bukkit.craftbukkit.v1_7_R4.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ArrayIndexOutOfBoundsException: -1
        at java.util.ArrayList.elementData(ArrayList.java:400)
        at java.util.ArrayList.get(ArrayList.java:413)
        at com.jofkos.signs.utils.Updater.getLast(Updater.java:106)
        at com.jofkos.signs.utils.Updater.run(Updater.java:51)
        at org.bukkit.craftbukkit.v1_7_R4.scheduler.CraftTask.run(CraftTask.java:71)
        at org.bukkit.craftbukkit.v1_7_R4.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
        ... 3 more