Roguelike Dungeons can create a client-side crash when a Minecraft client user types /help <page number> for a page which is supposed to show commands for Roguelike Dungeons. This is due to RLD returning null, instead of a string, for its usage. See the line here:

See the discord conversation here: https://discord.com/channels/708811478395912266/709156231394361384/1269548151967055955

Thanks to @sylph_ for the find.

Fixed in 5ef89fd.