--- before/task_import.py
+++ after/task_import.py
@@ -11,7 +11,9 @@
         raise ValueError('CSV requires task_id and title headers')
     tasks, seen = [], set()
     for row in reader:
-        task_id = int(row['task_id'])
+        task_id = row['task_id'].strip()
+        if not task_id:
+            raise ValueError('task_id must not be empty')
         if task_id in seen:
             raise ValueError('duplicate task_id: ' + str(task_id))
         seen.add(task_id)