diff --git a/rdagent/components/backtesting/results_db.py b/rdagent/components/backtesting/results_db.py
index 3c5105fd..b745c299 100644
--- a/rdagent/components/backtesting/results_db.py
+++ b/rdagent/components/backtesting/results_db.py
@@ -166,7 +166,7 @@ class ResultsDatabase:
         self.conn.commit()
         return c.lastrowid
     
-    def add_loop(self, loop_idx: int, success: int, fail: int, best_ic: float = None, status: str = "completed") -> int:
+    def add_loop(self, loop_idx: int, success: int, fail: int, best_ic: float | None = None, status: str = "completed") -> int:
         c = self.conn.cursor()
         rate = success / (success + fail) if (success + fail) > 0 else 0
         c.execute("""INSERT INTO loop_results (loop_index, factors_success, factors_fail, success_rate, best_ic, status)
diff --git a/rdagent/components/backtesting/vbt_backtest.py b/rdagent/components/backtesting/vbt_backtest.py
index 6c125a86..a5c20dc3 100644
--- a/rdagent/components/backtesting/vbt_backtest.py
+++ b/rdagent/components/backtesting/vbt_backtest.py
@@ -67,7 +67,6 @@ def _cross_check_with_vbt(
     close: pd.Series,
     position: pd.Series,
     txn_cost: float,
-    manual_total_return: float,
     freq: str,
 ) -> float | None:
     """Run a vectorbt simulation and return its total_return for comparison."""
@@ -264,7 +263,6 @@ def backtest_signal(
             close=close,
             position=position,
             txn_cost=txn_cost,
-            manual_total_return=total_return,
             freq=freq,
         )
 
diff --git a/rdagent/core/utils.py b/rdagent/core/utils.py
index cc35c017..0602dbb4 100644
--- a/rdagent/core/utils.py
+++ b/rdagent/core/utils.py
@@ -83,10 +83,24 @@ def import_class(class_path: str) -> Any:
     Returns
     -------
         class of `class_path`
+
+    Raises
+    ------
+    ImportError
+        If module or class cannot be found.
     """
-    module_path, class_name = class_path.rsplit(".", 1)
-    module = importlib.import_module(module_path)
-    return getattr(module, class_name)
+    try:
+        module_path, class_name = class_path.rsplit(".", 1)
+    except ValueError:
+        raise ImportError(f"Invalid class path: {class_path!r}")
+    try:
+        module = importlib.import_module(module_path)
+    except ModuleNotFoundError as e:
+        raise ImportError(f"Module not found: {module_path!r}") from e
+    try:
+        return getattr(module, class_name)
+    except AttributeError as e:
+        raise ImportError(f"Class not found: {class_name!r} in {module_path!r}") from e
 
 
 class CacheSeedGen: