Fix: empty file with better message (#15232)

Fix: empty file with better message

rag/svr/task_executor.py

@@ -273,6 +273,8 @@ async def build_chunks(task, progress_callback):
         st = timer()
         bucket, name = File2DocumentService.get_storage_address(doc_id=task["doc_id"])
         binary = await get_storage_binary(bucket, name)
+        if binary is None:
+            raise FileNotFoundError(f"File not found: storage returned no content for {bucket}/{name}.")
         logging.info("From minio({}) {}/{}".format(timer() - st, task["location"], task["name"]))
     except TimeoutError:
         progress_callback(-1, "Internal server error: Fetch file from minio timeout. Could you try it again.")