This presumably happens when viewing a replay while MoreCommands is installed.
java.lang.NullPointerException: null
at java.util.Objects.requireNonNull(Objects.java:203) ~[?:1.8.0_51]
at com.ptsmods.morecommands.MoreCommandsClient.getWorldName(MoreCommandsClient.java:191) ~[MoreCommands-3.4.2_1.16.5.jar:?]
at com.ptsmods.morecommands.MoreCommandsClient.updatePresence(MoreCommandsClient.java:201) ~[MoreCommands-3.4.2_1.16.5.jar:?]
Forwarding https://github.com/ReplayMod/ReplayMod/issues/514 which in turn was forwarded from Discord.
This presumably happens when viewing a replay while MoreCommands is installed.
latest (1).log
See https://github.com/ReplayMod/ReplayMod/issues/514#issuecomment-830440758 for a lengthy explanation of what is going on and why I think this should be fixed here rather than over there. TLDR: do not assume that singleplayer and multiplayer are the only options