add handling of empty responses

src/delta_barth/analysis/forecast.py

@@ -11,6 +11,7 @@ from xgboost import XGBRegressor
 from delta_barth.analysis import parse
 from delta_barth.api.requests import (
     SalesPrognosisResponse,
+    SalesPrognosisResponseEntry,
     SalesPrognosisResults,
     SalesPrognosisResultsExport,
     get_sales_prognosis_data,
@@ -50,6 +51,10 @@ def _parse_api_resp_to_df(
     """
     data = resp.model_dump()["daten"]
 
+    if not data:
+        target_features = SalesPrognosisResponseEntry.__annotations__.keys()
+        data = {feat: [] for feat in target_features}
+
     return pd.DataFrame(data)