Add debug message for weird crash.
@@ -536,8 +536,7 @@ class UiStateTracker {
Action action = event.getAction();
Artifact actionId = action.getPrimaryOutput();
- checkState(activeActions.containsKey(actionId));
- activeActions.remove(actionId);
+ checkNotNull(activeActions.remove(actionId), "%s %s", actionId, event);
if (action.getOwner() != null) {
Label owner = action.getOwner().getLabel();
