Revert feat(normalization): add validation for empty features in NormalizerProcessorStep and UnnormalizerProcessorStep (#2087)

Revert "feat(normalization): add validation for empty features in NormalizerProcessorStep and UnnormalizerProcessorStep (#2087)"

This reverts commit f173265354.

src/lerobot/processor/normalize_processor.py

@@ -108,18 +108,16 @@ class _NormalizationMixin:
         """
         # Track if stats were explicitly provided (not None and not empty)
         self._stats_explicitly_provided = self.stats is not None and bool(self.stats)
-        # Check if self.features is not empty
-        if not self.features:
-            raise ValueError("Normalization features cannot be empty")
         # Robust JSON deserialization handling (guard empty maps).
-        first_val = next(iter(self.features.values()))
-        if isinstance(first_val, dict):
-            reconstructed = {}
-            for key, ft_dict in self.features.items():
-                reconstructed[key] = PolicyFeature(
-                    type=FeatureType(ft_dict["type"]), shape=tuple(ft_dict["shape"])
-                )
-            self.features = reconstructed
+        if self.features:
+            first_val = next(iter(self.features.values()))
+            if isinstance(first_val, dict):
+                reconstructed = {}
+                for key, ft_dict in self.features.items():
+                    reconstructed[key] = PolicyFeature(
+                        type=FeatureType(ft_dict["type"]), shape=tuple(ft_dict["shape"])
+                    )
+                self.features = reconstructed
 
         # if keys are strings (JSON), rebuild enum map
         if self.norm_map and all(isinstance(k, str) for k in self.norm_map):

tests/policies/test_policies.py

@@ -234,6 +234,7 @@ def test_act_backbone_lr():
     assert cfg.policy.optimizer_lr_backbone == 0.001
 
     dataset = make_dataset(cfg)
+    preprocessor, _ = make_pre_post_processors(cfg.policy, None)
     policy = make_policy(cfg.policy, ds_meta=dataset.meta)
     optimizer, _ = make_optimizer_and_scheduler(cfg, policy)
     assert len(optimizer.param_groups) == 2

tests/processor/test_normalize_processor.py

@@ -534,18 +534,6 @@ def test_empty_observation():
     assert result == transition
 
 
-def test_empty_features_raises_error():
-    """Test that empty features dict raises ValueError."""
-    norm_map = {FeatureType.VISUAL: NormalizationMode.MEAN_STD}
-    stats = {OBS_IMAGE: {"mean": [0.5], "std": [0.2]}}
-
-    with pytest.raises(ValueError, match="Normalization features cannot be empty"):
-        NormalizerProcessorStep(features={}, norm_map=norm_map, stats=stats)
-
-    with pytest.raises(ValueError, match="Normalization features cannot be empty"):
-        UnnormalizerProcessorStep(features={}, norm_map=norm_map, stats=stats)
-
-
 def test_empty_stats():
     features = {OBS_IMAGE: PolicyFeature(FeatureType.VISUAL, (3, 96, 96))}
     norm_map = {FeatureType.VISUAL: NormalizationMode.MEAN_STD}