Bukkit

[What steps will reproduce the problem?]
1. Create a Custom Player Skull
====
/give @p skull 1 3 {display:{Name:"Wood Plank"},SkullOwner:{Id:"01e7a0b0-cd34-44fa-9090-eeed6f93ccec",Properties:{textures:[{Value:"eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvYTBlOWQyYmViODRiMzJlM2YxNWUzODBjYzJjNTUxMDY0MjkxMWE1MTIxMDVmYTJlYzY3OWJjNTQwZmQ4MTg0In19fQ=="}]}}}
====
2. Use /iinfo

[What version of the plugin are you using?
v3.8.7

[What version of the CraftBukkit are you using?
Spigot 1.8.3

[What economy plugin are you using?
Fe 0.8.2

[Do you have an error log of what happened? Check your console, server.log and messages you got through chat]
null
org.bukkit.command.CommandException: Unhandled exception executing command 'iinfo' in plugin ChestShop v3.8.7
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.bukkit.craftbukkit.v1_8_R2.CraftServer.dispatchCommand(CraftServer.java:646) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at net.minecraft.server.v1_8_R2.PlayerConnection.handleCommand(PlayerConnection.java:1133) [craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at net.minecraft.server.v1_8_R2.PlayerConnection.a(PlayerConnection.java:968) [craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at net.minecraft.server.v1_8_R2.PacketPlayInChat.a(PacketPlayInChat.java:45) [craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at net.minecraft.server.v1_8_R2.PacketPlayInChat.a(PacketPlayInChat.java:1) [craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at net.minecraft.server.v1_8_R2.PlayerConnectionUtils$1.run(SourceFile:13) [craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.7.0_71]
    at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.7.0_71]
    at net.minecraft.server.v1_8_R2.SystemUtils.a(SourceFile:60) [craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at net.minecraft.server.v1_8_R2.MinecraftServer.A(MinecraftServer.java:710) [craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at net.minecraft.server.v1_8_R2.DedicatedServer.A(DedicatedServer.java:368) [craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at net.minecraft.server.v1_8_R2.MinecraftServer.z(MinecraftServer.java:651) [craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at net.minecraft.server.v1_8_R2.MinecraftServer.run(MinecraftServer.java:554) [craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at java.lang.Thread.run(Unknown Source) [?:1.7.0_71]
Caused by: java.lang.NullPointerException: null value in entry: skull-owner=null
    at com.google.common.collect.CollectPreconditions.checkEntryNotNull(CollectPreconditions.java:33) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at com.google.common.collect.ImmutableMap.entryOf(ImmutableMap.java:135) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at com.google.common.collect.ImmutableMap$Builder.put(ImmutableMap.java:206) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.bukkit.craftbukkit.v1_8_R2.inventory.CraftMetaSkull.serialize(CraftMetaSkull.java:150) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.bukkit.craftbukkit.v1_8_R2.inventory.CraftMetaItem.serialize(CraftMetaItem.java:843) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.bukkit.configuration.file.YamlRepresenter$RepresentConfigurationSerializable.representData(YamlRepresenter.java:33) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.yaml.snakeyaml.representer.BaseRepresenter.representData(BaseRepresenter.java:95) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.yaml.snakeyaml.representer.BaseRepresenter.representMapping(BaseRepresenter.java:157) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.yaml.snakeyaml.representer.SafeRepresenter$RepresentMap.representData(SafeRepresenter.java:320) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.bukkit.configuration.file.YamlRepresenter$RepresentConfigurationSerializable.representData(YamlRepresenter.java:35) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.yaml.snakeyaml.representer.BaseRepresenter.representData(BaseRepresenter.java:95) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.yaml.snakeyaml.representer.BaseRepresenter.represent(BaseRepresenter.java:65) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.yaml.snakeyaml.Yaml.dumpAll(Yaml.java:271) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.yaml.snakeyaml.Yaml.dumpAll(Yaml.java:262) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.yaml.snakeyaml.Yaml.dumpAll(Yaml.java:234) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at org.yaml.snakeyaml.Yaml.dump(Yaml.java:209) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    at com.Acrobot.ChestShop.Metadata.ItemDatabase.getItemCode(ItemDatabase.java:70) ~[?:?]
    at com.Acrobot.Breeze.Utils.MaterialUtil$Metadata.getItemCode(MaterialUtil.java:358) ~[?:?]
    at com.Acrobot.ChestShop.Commands.ItemInfo.getMetadata(ItemInfo.java:69) ~[?:?]
    at com.Acrobot.ChestShop.Commands.ItemInfo.onCommand(ItemInfo.java:39) ~[?:?]
    at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[craftbukkit.jar:git-Spigot-dbe012b-61ef214]
    ... 15 more

I'm sorry, but it appears to be an error caused by data of the skull you are giving to yourself.

"java.lang.NullPointerException null value in entry: skull-owner=null"

(It comes from Bukkit, not ChestShop).