when i tried i got this error in the server console
[Server thread/ERROR]: Failed to handle packet net.minecraft.class_2805@213502dd, suppressing error
java.lang.NullPointerException: Cannot invoke "net.minecraft.class_2960.method_12836()" because "$$6" is null
at knot/net.minecraft.class_2172.method_9268(class_2172.java:124) ~[server-intermediary.jar:?]
at knot/eu.pb4.polymer.core.impl.Commands.lambda$register$1(Commands.java:111) ~[polymer-core-0.13.1+1.21.6-ed67e2a6ab073ee2.jar:?]
at knot/com.mojang.brigadier.tree.ArgumentCommandNode.listSuggestions(ArgumentCommandNode.java:71) ~[brigadier-1.3.10.jar:?]
at knot/com.mojang.brigadier.CommandDispatcher.getCompletionSuggestions(CommandDispatcher.java:541) ~[brigadier-1.3.10.jar:?]
at knot/com.mojang.brigadier.CommandDispatcher.getCompletionSuggestions(CommandDispatcher.java:523) ~[brigadier-1.3.10.jar:?]
at knot/net.minecraft.class_3244.method_12059(class_3244.java:590) ~[server-intermediary.jar:?]
at knot/net.minecraft.class_2805.method_12147(class_2805.java:37) ~[server-intermediary.jar:?]
at knot/net.minecraft.class_2805.method_65081(class_2805.java:9) ~[server-intermediary.jar:?]
at knot/net.minecraft.class_2600.method_11072(class_2600.java:27) ~[server-intermediary.jar:?]
at knot/net.minecraft.class_3738.run(class_3738.java:18) ~[server-intermediary.jar:?]
at knot/net.minecraft.class_1255.method_18859(class_1255.java:164) ~[server-intermediary.jar:?]
at knot/net.minecraft.class_4093.method_18859(class_4093.java:23) ~[server-intermediary.jar:?]
at knot/net.minecraft.server.MinecraftServer.method_24306(MinecraftServer.java:883) ~[server-intermediary.jar:?]
at knot/net.minecraft.server.MinecraftServer.method_18859(MinecraftServer.java:179) ~[server-intermediary.jar:?]
at knot/net.minecraft.class_1255.method_16075(class_1255.java:138) ~[server-intermediary.jar:?]
at knot/net.minecraft.server.MinecraftServer.method_20415(MinecraftServer.java:865) ~[server-intermediary.jar:?]
at knot/net.minecraft.server.MinecraftServer.method_16075(MinecraftServer.java:859) ~[server-intermediary.jar:?]
at knot/net.minecraft.class_1255.method_18857(class_1255.java:147) ~[server-intermediary.jar:?]
at knot/net.minecraft.server.MinecraftServer.method_18857(MinecraftServer.java:823) ~[server-intermediary.jar:?]
at knot/net.minecraft.server.MinecraftServer.method_16208(MinecraftServer.java:830) ~[server-intermediary.jar:?]
at knot/net.minecraft.server.MinecraftServer.method_29741(MinecraftServer.java:713) ~[server-intermediary.jar:?]
at knot/net.minecraft.server.MinecraftServer.method_29739(MinecraftServer.java:291) ~[server-intermediary.jar:?]
at java.base/java.lang.Thread.run(Thread.java:1583) [?:?]