Add clarifying comment for nil session handling

Co-authored-by: hsluoyz <3787410+hsluoyz@users.noreply.github.com>

object/session.go

@@ -175,8 +175,10 @@ func DeleteSession(id, curSessionId string) (bool, error) {
 			return false, err
 		}
 
+		// If session doesn't exist, return success with no rows affected
+		// This is a valid state (e.g., when a user has no active session)
 		if session == nil {
-			return false, fmt.Errorf("session is nil")
+			return false, nil
 		}
 
 		if slices.Contains(session.SessionId, curSessionId) {