fix: guard against empty df in regression fallback and preprocessing

Author: JMR825

backend/app/services/preprocessing.py

@@ -72,6 +72,8 @@ def add_momentum(df: pd.DataFrame, window: int = 10) -> pd.DataFrame:
 
 def preprocess_symbol_data(df: pd.DataFrame, period_type: str = "daily") -> pd.DataFrame:
     """Full preprocessing pipeline for a single symbol with adaptive windows."""
+    if df is None or df.empty or len(df) < 2:
+        return pd.DataFrame()
     data = clean_price_data(df)
     data = add_returns(data)
 

backend/app/services/regression_predictor.py

@@ -154,7 +154,16 @@ def predict_all_regression(
             )
             comparisons[symbol] = result["model_comparison"]
         except (ValueError, Exception):
-            # Fallback: use recent momentum as simple prediction
+            if len(df) == 0:
+                predictions.append({
+                    "symbol": symbol,
+                    "latest_price": 0.0,
+                    "predicted_return": 0.0,
+                    "trend": "neutral",
+                    "confidence": 0.0,
+                    "model_used": "no_data_fallback",
+                })
+                continue
             mom = float(df["momentum"].iloc[-1]) if "momentum" in df.columns else 0.0
             predictions.append(
                 {