Minor error

[17:50:48 WARN]: [RailMiner] Task #11570 for RailMiner v1.1 generated an exception
java.lang.NullPointerException
        at org.bukkit.craftbukkit.v1_8_R3.block.CraftSign.update(CraftSign.java:56) ~[spigot-1.8.8.jar:git-Spigot-21fe707-e1ebe52]
        at org.bukkit.craftbukkit.v1_8_R3.block.CraftBlockState.update(CraftBlockState.java:148) ~[spigot-1.8.8.jar:git-Spigot-21fe707-e1ebe52]
        at org.bukkit.craftbukkit.v1_8_R3.block.CraftBlockState.update(CraftBlockState.java:144) ~[spigot-1.8.8.jar:git-Spigot-21fe707-e1ebe52]
        at me.bumblebee.railminer.Miner.setSignStatus(Miner.java:328) ~[?:?]
        at me.bumblebee.railminer.Miner$1.run(Miner.java:227) ~[?:?]
        at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java:71) ~[spigot-1.8.8.jar:git-Spigot-21fe707-e1ebe52]
        at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:350) [spigot-1.8.8.jar:git-Spigot-21fe707-e1ebe52]
        at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:723) [spigot-1.8.8.jar:git-Spigot-21fe707-e1ebe52]
        at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:374) [spigot-1.8.8.jar:git-Spigot-21fe707-e1ebe52]
        at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:654) [spigot-1.8.8.jar:git-Spigot-21fe707-e1ebe52]
        at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:557) [spigot-1.8.8.jar:git-Spigot-21fe707-e1ebe52]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_111]