fix(STEF-2802): skip RollingAggregatesAdder when no aggregation functions (#813)

When rolling_aggregate_features is empty (e.g., ato_regions, grid_losses),
the RollingAggregatesAdder transform is no longer added to the pipeline.
Previously it was always added, and fit() would crash with
ValueError: No objects to concatenate when calling pandas rolling().agg([]).

Signed-off-by: Egor Dmitriev <[email protected]>

Author: egordm

packages/openstef-models/src/openstef_models/presets/forecasting_workflow.py

@@ -305,10 +305,16 @@ def create_forecasting_workflow(config: ForecastingWorkflowConfig) -> CustomFore
         DaylightFeatureAdder(
             coordinate=config.location.coordinate,
         ),
-        RollingAggregatesAdder(
-            feature=config.target_column,
-            aggregation_functions=config.rolling_aggregate_features,
-            horizons=config.horizons,
+        *(
+            [
+                RollingAggregatesAdder(
+                    feature=config.target_column,
+                    aggregation_functions=config.rolling_aggregate_features,
+                    horizons=config.horizons,
+                ),
+            ]
+            if config.rolling_aggregate_features
+            else []
         ),
     ]
     feature_standardizers = [