diff --git a/src/dflow/python/opio.py b/src/dflow/python/opio.py
index 2ee946c3..e75991ef 100644
--- a/src/dflow/python/opio.py
+++ b/src/dflow/python/opio.py
@@ -33,8 +33,11 @@ def dataset(self):
     def __deepcopy__(self, memo=None):
         return self
 
+    def is_none(self):
+        return self.dataset.attrs.get("type") == "null"
+
     def get_data(self):
-        if self.dataset.attrs.get("type") == "null":
+        if self.is_none():
             return None
         data = self.dataset[()]
         if self.dataset.attrs.get("dtype") == "utf-8":
diff --git a/src/dflow/python/utils.py b/src/dflow/python/utils.py
index c4204752..7a055670 100644
--- a/src/dflow/python/utils.py
+++ b/src/dflow/python/utils.py
@@ -101,7 +101,10 @@ def handle_input_artifact(name, sign, slices=None, data_root="/tmp",
         res = []
         for path in path_object:
             f = h5py.File(path, "r")
-            datasets = {k: HDF5Dataset(f, k) for k in f.keys()}
+            datasets = {}
+            for k in f.keys():
+                d = HDF5Dataset(f, k)
+                datasets[k] = None if d.is_none() else d
             if set(datasets.keys()) == {str(i) for i in range(len(datasets))} \
                     and isinstance(res, list):
                 # concat when all datasets are lists