Server log

[22:41:07 INFO]: ViiPy issued server command: /manuadd Deaththeboy lord world
[22:41:07 ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'manuadd' in plugin GroupManager vPre2.14.1.3 FINAL (Phoenix)
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[craftbukkit.jar:git-Bukkit-12698ea]
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:140) ~[craftbukkit.jar:git-Bukkit-12698ea]
at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchCommand(CraftServer.java:620) ~[craftbukkit.jar:git-Bukkit-12698ea]
at net.minecraft.server.v1_8_R3.PlayerConnection.handleCommand(PlayerConnection.java:1106) [craftbukkit.jar:git-Bukkit-12698ea]
at net.minecraft.server.v1_8_R3.PlayerConnection.a(PlayerConnection.java:966) [craftbukkit.jar:git-Bukkit-12698ea]
at net.minecraft.server.v1_8_R3.PacketPlayInChat.a(SourceFile:37) [craftbukkit.jar:git-Bukkit-12698ea]
at net.minecraft.server.v1_8_R3.PacketPlayInChat.a(SourceFile:9) [craftbukkit.jar:git-Bukkit-12698ea]
at net.minecraft.server.v1_8_R3.PlayerConnectionUtils$1.run(SourceFile:13) [craftbukkit.jar:git-Bukkit-12698ea]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_101]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_101]
at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:44) [craftbukkit.jar:git-Bukkit-12698ea]
at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:673) [craftbukkit.jar:git-Bukkit-12698ea]
at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:335) [craftbukkit.jar:git-Bukkit-12698ea]
at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:629) [craftbukkit.jar:git-Bukkit-12698ea]
at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:537) [craftbukkit.jar:git-Bukkit-12698ea]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_101]
Caused by: java.lang.IllegalArgumentException: Name cannot be null
at org.apache.commons.lang.Validate.notNull(Validate.java:192) ~[craftbukkit.jar:git-Bukkit-12698ea]
at org.bukkit.craftbukkit.v1_8_R3.CraftServer.getPlayer(CraftServer.java:388) ~[craftbukkit.jar:git-Bukkit-12698ea]
at org.bukkit.Bukkit.getPlayer(Bukkit.java:383) ~[craftbukkit.jar:git-Bukkit-12698ea]
at org.anjocaido.groupmanager.data.User.getBukkitPlayer(User.java:319) ~[?:?]
at org.anjocaido.groupmanager.data.User.setGroup(User.java:183) ~[?:?]
at org.anjocaido.groupmanager.data.User.setGroup(User.java:164) ~[?:?]
at org.anjocaido.groupmanager.GroupManager.onCommand(GroupManager.java:551) ~[?:?]
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[craftbukkit.jar:git-Bukkit-12698ea]
... 15 more