Console error everytime server goes off

[ghost]

[12:49:52] [Server thread/ERROR]: Error occurred while disabling DungeonsXL v0.15.6 (Is it up to date?) java.lang.NullPointerException at io.github.dre2n.dungeonsxl.global.GroupSign.save(GroupSign.java:232) ~[?:?] at io.github.dre2n.dungeonsxl.global.GlobalProtections.saveAll(GlobalProtections.java:119) ~[?:?] at io.github.dre2n.dungeonsxl.global.GlobalProtections.saveAll(GlobalProtections.java:101) ~[?:?] at io.github.dre2n.dungeonsxl.DungeonsXL.saveData(DungeonsXL.java:286) ~[?:?] at io.github.dre2n.dungeonsxl.DungeonsXL.onDisable(DungeonsXL.java:171) ~[?:?] at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:273) ~[server.jar:git-Paper-1104] at org.bukkit.plugin.java.JavaPluginLoader.disablePlugin(JavaPluginLoader.java:344) [server.jar:git-Paper-1104] at org.bukkit.plugin.SimplePluginManager.disablePlugin(SimplePluginManager.java:427) [server.jar:git-Paper-1104] at org.bukkit.plugin.SimplePluginManager.disablePlugins(SimplePluginManager.java:420) [server.jar:git-Paper-1104] at org.bukkit.craftbukkit.v1_11_R1.CraftServer.disablePlugins(CraftServer.java:347) [server.jar:git-Paper-1104] at net.minecraft.server.v1_11_R1.MinecraftServer.stop(MinecraftServer.java:482) [server.jar:git-Paper-1104] at net.minecraft.server.v1_11_R1.MinecraftServer.run(MinecraftServer.java:697) [server.jar:git-Paper-1104] at java.lang.Thread.run(Thread.java:748) [?:1.8.0_131]