Error message

[14:29:58 INFO]: GamingTechnology issued server command: /bedwars joinNPC spawn SOLO GamingTechnology Click to join;SOLO;playersPlayin
[14:29:58 ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing 'bedwars joinNPC spawn SOLO GamingTechnology Click to join;SOLO;playersPlayin' in ro.marius.bedwars.commands.BedwarsCommand(bedwars)
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:148) ~[Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        at org.bukkit.craftbukkit.v1_8_R1.CraftServer.dispatchCommand(CraftServer.java:646) ~[Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        at net.minecraft.server.v1_8_R1.PlayerConnection.handleCommand(PlayerConnection.java:1115) [Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        at net.minecraft.server.v1_8_R1.PlayerConnection.a(PlayerConnection.java:950) [Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        at net.minecraft.server.v1_8_R1.PacketPlayInChat.a(PacketPlayInChat.java:26) [Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        at net.minecraft.server.v1_8_R1.PacketPlayInChat.a(PacketPlayInChat.java:53) [Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        at net.minecraft.server.v1_8_R1.PacketHandleTask.run(SourceFile:13) [Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_51]
        at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_51]
        at net.minecraft.server.v1_8_R1.MinecraftServer.z(MinecraftServer.java:696) [Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        at net.minecraft.server.v1_8_R1.DedicatedServer.z(DedicatedServer.java:316) [Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        at net.minecraft.server.v1_8_R1.MinecraftServer.y(MinecraftServer.java:634) [Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        at net.minecraft.server.v1_8_R1.MinecraftServer.run(MinecraftServer.java:537) [Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        at java.lang.Thread.run(Thread.java:745) [?:1.8.0_51]
Caused by: java.lang.NoClassDefFoundError: net/citizensnpcs/api/CitizensAPI
        at ro.marius.bedwars.manager.type.NPCManager.spawnNPC(NPCManager.java:37) ~[?:?]
        at ro.marius.bedwars.commands.subcommand.NPCommand.onCommand(NPCommand.java:62) ~[?:?]
        at ro.marius.bedwars.commands.BedwarsCommand.onCommand(BedwarsCommand.java:746) ~[?:?]
        at ro.marius.bedwars.commands.AbstractCommand.execute(AbstractCommand.java:16) ~[?:?]
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) ~[Spigot_1.8.jar:git-Spigot-c3c767f-33d5de3]
        ... 13 more