diff --git a/be/app/config.py b/be/app/config.py
index b5ef157..ffa6e0d 100644
--- a/be/app/config.py
+++ b/be/app/config.py
@@ -98,6 +98,12 @@ Organic Bananas
     HTTP_500_DETAIL: str = "Internal Server Error"
     HTTP_503_DETAIL: str = "Service Unavailable"
 
+    # --- Database Error Messages ---
+    DB_CONNECTION_ERROR: str = "Database connection error"
+    DB_INTEGRITY_ERROR: str = "Database integrity error"
+    DB_TRANSACTION_ERROR: str = "Database transaction error"
+    DB_QUERY_ERROR: str = "Database query error"
+
     class Config:
         env_file = ".env"
         env_file_encoding = 'utf-8'
diff --git a/be/app/core/exceptions.py b/be/app/core/exceptions.py
index dd7c303..7d34b38 100644
--- a/be/app/core/exceptions.py
+++ b/be/app/core/exceptions.py
@@ -122,10 +122,10 @@ class DatabaseTransactionError(HTTPException):
 
 class DatabaseQueryError(HTTPException):
     """Raised when a database query fails."""
-    def __init__(self):
+    def __init__(self, detail: str = settings.DB_QUERY_ERROR):
         super().__init__(
             status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
-            detail=settings.DB_QUERY_ERROR
+            detail=detail
         )
 
 class OCRServiceUnavailableError(HTTPException):
diff --git a/be/app/crud/list.py b/be/app/crud/list.py
index b674563..f289662 100644
--- a/be/app/crud/list.py
+++ b/be/app/crud/list.py
@@ -51,18 +51,22 @@ async def get_lists_for_user(db: AsyncSession, user_id: int) -> PyList[ListModel
             )
             user_group_ids = group_ids_result.scalars().all()
 
-            query = select(ListModel).where(
-                or_(
-                    and_(ListModel.created_by_id == user_id, ListModel.group_id == None),
-                    ListModel.group_id.in_(user_group_ids)
-                )
-            ).order_by(ListModel.updated_at.desc())
+            # Build conditions for the OR clause dynamically
+            conditions = [
+                and_(ListModel.created_by_id == user_id, ListModel.group_id.is_(None))
+            ]
+            if user_group_ids:  # Only add the IN clause if there are group IDs
+                conditions.append(ListModel.group_id.in_(user_group_ids))
+
+            query = select(ListModel).where(or_(*conditions)).order_by(ListModel.updated_at.desc())
 
             result = await db.execute(query)
             return result.scalars().all()
     except OperationalError as e:
         raise DatabaseConnectionError(f"Failed to connect to database: {str(e)}")
     except SQLAlchemyError as e:
+        # It would be helpful to log the original error e here for more detailed debugging
+        # For example: logger.error(f"SQLAlchemyError in get_lists_for_user: {type(e).__name__} - {str(e)}")
         raise DatabaseQueryError(f"Failed to query user lists: {str(e)}")
 
 async def get_list_by_id(db: AsyncSession, list_id: int, load_items: bool = False) -> Optional[ListModel]: