Launcher problems

HMCL Crash: When whenComplete succeeded, Task.exception must be null

What the log looks like

java\.lang\.AssertionError: When whenComplete succeeded, Task\.exception must be null\.
When whenComplete succeeded, Task\.exception must be null\.[\s\S]{0,120}org\.jackhuang\.hmcl\.task\.Task

How to fix it

  1. Update HMCL to the latest stable or development version (3.5.4 or newer), which contains the official fix for this task-handling bug.
  2. Restart HMCL completely if the mod update or modpack download window is stuck on screen and refuses to cancel.
  3. If network timeouts persist while downloading modpacks or checking mod updates, change the download mirror in HMCL Settings -> Download or update mods individually instead of all at once.
LoadersVanilla, Forge, Neoforge, Fabric, Quilt
SeverityBreaks something
CategoryLauncher problems

Check your own log

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