Update ace.py

ace.py

@@ -55,8 +55,8 @@ class MockupDataset(datasets.GeneratorBasedBuilder):
     def _info(self):
         features = datasets.Features(
             {
-                "x": datasets.Value("null"),
-                "y": datasets.Value("null")
+                "x": datasets.Sequence(datasets.Value("int32"), length=-1),
+                "y": datasets.Sequence(datasets.Value("int32"), length=-1)
             }
         )