There are some problems:

[18:13:12 ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'clan' in plugin Clans v1.1
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:47) ~[patched_1.16.5.jar:git-Paper-794]
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:159) ~[patched_1.16.5.jar:git-Paper-794]
at org.bukkit.craftbukkit.v1_16_R3.CraftServer.dispatchCommand(CraftServer.java:826) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.PlayerConnection.handleCommand(PlayerConnection.java:2185) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.PlayerConnection.c(PlayerConnection.java:2000) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.PlayerConnection.a(PlayerConnection.java:1953) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.PacketPlayInChat.a(PacketPlayInChat.java:49) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.PacketPlayInChat.a(PacketPlayInChat.java:7) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.PlayerConnectionUtils.lambda$ensureMainThread$1(PlayerConnectionUtils.java:35) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.TickTask.run(SourceFile:18) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.IAsyncTaskHandler.executeTask(IAsyncTaskHandler.java:136) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.IAsyncTaskHandler.executeNext(IAsyncTaskHandler.java:109) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.MinecraftServer.bb(MinecraftServer.java:1271) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.MinecraftServer.executeNext(MinecraftServer.java:1264) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.IAsyncTaskHandler.awaitTasks(IAsyncTaskHandler.java:119) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.MinecraftServer.sleepForTick(MinecraftServer.java:1225) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.MinecraftServer.w(MinecraftServer.java:1139) ~[patched_1.16.5.jar:git-Paper-794]
at net.minecraft.server.v1_16_R3.MinecraftServer.lambda$a$0(MinecraftServer.java:291) ~[patched_1.16.5.jar:git-Paper-794]
at java.lang.Thread.run(Thread.java:840) [?:?]
Caused by: java.lang.IndexOutOfBoundsException: No group 1
at java.util.regex.Matcher.start(Matcher.java:482) ~[?:?]
at java.util.regex.Matcher.appendExpandedReplacement(Matcher.java:1090) ~[?:?]
at java.util.regex.Matcher.appendReplacement(Matcher.java:997) ~[?:?]
at java.util.regex.Matcher.replaceAll(Matcher.java:1181) ~[?:?]
at java.lang.String.replaceAll(String.java:2944) ~[?:?]
at flowxrc.clans.Utilities.replacePlaceholders(Utilities.java:55) ~[?:?]
at flowxrc.clans.Commands.CreateCommand.execute(CreateCommand.java:56) ~[?:?]
at flowxrc.clans.Commands.ClanCommand.onCommand(ClanCommand.java:53) ~[?:?]
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:45) ~[patched_1.16.5.jar:git-Paper-794]
... 19 more