"bad packet id 26" upon connecting after tempban expire

This can be reproduced similarly to MC-84786

That is, apply a tempban with an expire time and then connect after it expires.

I have submitted a patch to Paper that Mojang is free to use - https://github.com/PaperMC/Paper/pull/2458

(the code is a bit different due to CraftBukkit changes but the same logic applies)

The relevant code is just this one line (spigot mappings), marked // NPE in PlayerList:

if (this.k.isBanned(gameprofile)) {
            GameProfileBanEntry gameprofilebanentry = (GameProfileBanEntry) this.k.get(gameprofile);

            chatmessage = new ChatMessage("multiplayer.disconnect.banned.reason", new Object[]{gameprofilebanentry.getReason()}); // NPE
            if (gameprofilebanentry.getExpires() != null) {
                chatmessage.addSibling(new ChatMessage("multiplayer.disconnect.banned.expiration", new Object[]{PlayerList.g.format(gameprofilebanentry.getExpires())}));
            }

the get() call will remove the relevant entry if it has expired, and then return null.  Then it will clearly NPE on the marked line.

The stacktrace of this occurring on the vanilla server:

[06:30:45] [Server thread/WARN]: Failed to handle packet for /127.0.0.1:50701
java.lang.NullPointerException: null
        at xv.a(SourceFile:357) ~[minecraft_server.jar:?]
        at we.c(SourceFile:97) ~[minecraft_server.jar:?]
        at we.b(SourceFile:63) ~[minecraft_server.jar:?]
        at jc.a(SourceFile:230) ~[minecraft_server.jar:?]
        at wb.c(SourceFile:171) [minecraft_server.jar:?]
        at net.minecraft.server.MinecraftServer.b(SourceFile:847) [minecraft_server.jar:?]
        at uk.b(SourceFile:343) [minecraft_server.jar:?]
        at net.minecraft.server.MinecraftServer.a(SourceFile:774) [minecraft_server.jar:?]
        at net.minecraft.server.MinecraftServer.run(SourceFile:642) [minecraft_server.jar:?]
        at java.lang.Thread.run(Thread.java:748) [?:1.8.0_222]
[06:30:45] [Server thread/INFO]: com.mojang.authlib.GameProfile@664932ca[id=9a9949cc-1987-3d04-b56b-cf3286adfe51,name=searchndstroy,properties={},legacy=false] (/127.0.0.1:50701) lost connection: Internal server error