Bukkit

That is just console spam. Spawners work properly.

[CustomSpawners] Task #33 for CustomSpawners v0.4.1 generated an exception
java.lang.NullPointerException
at com.github.thebiologist13.Spawner.spawn(Spawner.java:675)
at com.github.thebiologist13.Spawner.spawn(Spawner.java:662)
at com.github.thebiologist13.Spawner.tick(Spawner.java:707)
at com.github.thebiologist13.CustomSpawners$1.run(CustomSpawners.java:1199)
at org.bukkit.craftbukkit.v1_5_R3.scheduler.CraftTask.run(CraftTask.java:53)
at org.bukkit.craftbukkit.v1_5_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:345)
at net.minecraft.server.v1_5_R3.MinecraftServer.r(MinecraftServer.java:513)
at net.minecraft.server.v1_5_R3.DedicatedServer.r(DedicatedServer.java:226)
at net.minecraft.server.v1_5_R3.MinecraftServer.q(MinecraftServer.java:477)
at net.minecraft.server.v1_5_R3.MinecraftServer.run(MinecraftServer.java:410)
at net.minecraft.server.v1_5_R3.ThreadServerApplication.run(SourceFile:573)