Stack Trace, Creeper spawn

java.lang.Exception: Stack trace
        at java.lang.Thread.dumpStack(Unknown Source)
        at MobSpawnDetector$Detector.onMobSpawn(MobSpawnDetector.java:27)
        at PluginLoader.callHook(PluginLoader.java:569)
        at OWorldServer.b(OWorldServer.java:128)
        at OSpawnerAnimals.a(SourceFile:148)
        at OWorld.h(SourceFile:1474)
        at net.minecraft.server.MinecraftServer.h(SourceFile:347)
        at net.minecraft.server.MinecraftServer.run(SourceFile:286)
        at OThreadServerApplication.run(SourceFile:394)