NullPointerException while using command 'class attr'

[CharlyZhu]

This error occured when command 'class attr' was being used:
null
org.bukkit.command.CommandException: Unhandled exception executing 'class attr' in class
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:148) ~[spigot.jar:git-Spigot-642f6d2-6103339]
at org.bukkit.craftbukkit.v1_12_R1.CraftServer.dispatchCommand(CraftServer.java:648) ~[spigot.jar:git-Spigot-642f6d2-6103339]
at net.minecraft.server.v1_12_R1.PlayerConnection.handleCommand(PlayerConnection.java:1397) ~[spigot.jar:git-Spigot-642f6d2-6103339]
at net.minecraft.server.v1_12_R1.PlayerConnection.chat(PlayerConnection.java:1313) ~[spigot.jar:git-Spigot-642f6d2-6103339]
at org.bukkit.craftbukkit.v1_12_R1.entity.CraftPlayer.chat(CraftPlayer.java:239) ~[spigot.jar:git-Spigot-642f6d2-6103339]
at me.skymc.taboomenu.iconcommand.impl.IconCommandOp.execute(IconCommandOp.java:23) ~[?:?]
at me.skymc.taboomenu.display.Icon.lambda$null$3(Icon.java:190) ~[?:?]
at java.util.ArrayList.forEach(Unknown Source) ~[?:1.8.0_131]
at me.skymc.taboomenu.display.Icon.lambda$executeCommand$4(Icon.java:190) ~[?:?]
at org.bukkit.craftbukkit.v1_12_R1.scheduler.CraftTask.run(CraftTask.java:76) [spigot.jar:git-Spigot-642f6d2-6103339]
at org.bukkit.craftbukkit.v1_12_R1.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:361) [spigot.jar:git-Spigot-642f6d2-6103339]
at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:739) [spigot.jar:git-Spigot-642f6d2-6103339]
at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:406) [spigot.jar:git-Spigot-642f6d2-6103339]
at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:679) [spigot.jar:git-Spigot-642f6d2-6103339]
at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:577) [spigot.jar:git-Spigot-642f6d2-6103339]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_131]
Caused by: java.lang.NullPointerException
at com.sucy.skill.api.player.PlayerData.filter(PlayerData.java:530) ~[?:?]
at com.sucy.skill.api.player.PlayerData.openAttributeMenu(PlayerData.java:514) ~[?:?]
at com.sucy.skill.cmd.CmdAttribute.execute(CmdAttribute.java:68) ~[?:?]
at com.rit.sucy.commands.ConfigurableCommand.execute(ConfigurableCommand.java:550) ~[?:?]
at com.rit.sucy.commands.ConfigurableCommand.execute(ConfigurableCommand.java:558) ~[?:?]
at com.rit.sucy.commands.ConfigurableCommand.execute(ConfigurableCommand.java:516) ~[?:?]
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) ~[spigot.jar:git-Spigot-642f6d2-6103339]
... 15 more

After debugging with your source code, I think the problem comes from the PlayerData class:
512 ItemStack icon = manager.getAttribute(key).getIcon().clone();
513 ItemMeta meta = icon.getItemMeta();
514 meta.setDisplayName(filter(meta.getDisplayName(), key));
the icon fetched may not have a display name?