This server is running Paper version git-Paper-105 (MC: 1.15.2) (Implementing API version 1.15.2-R0.1-SNAPSHOT

Steps to reproduce:
Player Set Bounty on owner
owner remove bounty with "/mh bounty remove owner player"
player tries to set bounty again

org.bukkit.command.CommandException: Unhandled exception executing command 'mobhunt' in plugin MobHunting v7.0.0
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:47) ~[patched_1.15.2.jar:git-Paper-105]
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:159) ~[patched_1.15.2.jar:git-Paper-105]
at org.bukkit.craftbukkit.v1_15_R1.CraftServer.dispatchCommand(CraftServer.java:742) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.PlayerConnection.handleCommand(PlayerConnection.java:1821) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.PlayerConnection.a(PlayerConnection.java:1629) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.PacketPlayInChat.a(PacketPlayInChat.java:47) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.PacketPlayInChat.a(PacketPlayInChat.java:5) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.PlayerConnectionUtils.lambda$ensureMainThread$0(PlayerConnectionUtils.java:23) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.TickTask.run(SourceFile:18) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.executeTask(IAsyncTaskHandler.java:136) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.executeNext(IAsyncTaskHandler.java:109) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.MinecraftServer.ba(MinecraftServer.java:1038) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.MinecraftServer.executeNext(MinecraftServer.java:1031) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.awaitTasks(IAsyncTaskHandler.java:119) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.MinecraftServer.sleepForTick(MinecraftServer.java:1015) ~[patched_1.15.2.jar:git-Paper-105]
at net.minecraft.server.v1_15_R1.MinecraftServer.run(MinecraftServer.java:938) ~[patched_1.15.2.jar:git-Paper-105]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_242]
Caused by: java.lang.NullPointerException
at one.lindegaard.MobHunting.bounty.BountyManager.save(BountyManager.java:304) ~[?:?]
at one.lindegaard.MobHunting.commands.BountyCommand.onCommand(BountyCommand.java:198) ~[?:?]
at one.lindegaard.MobHunting.commands.CommandDispatcher.onCommand(CommandDispatcher.java:97) ~[?:?]
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:45) ~[patched_1.15.2.jar:git-Paper-105]
... 17 more

You should only write

"/mh bounty remove playername"

No response