Enhance data processing and utility functions

- Updated `process_price_change` to accept an optional `asset_id` parameter for better asset validation.
- Modified `process_data` to ensure `json_datas` is always a list and to pass `asset_id` when available.
- Added checks in `update_markets` to ensure the 'multiplier' column exists and fill NaN values with empty strings.
- Refactored multiplier application in `get_buy_sell_amount` to use `row.get()` for safer access.

poly_data/data_utils.py

@@ -149,6 +149,12 @@ def update_markets():
     received_df, received_params = get_sheet_df()
 
     if len(received_df) > 0:
+        # Ensure multiplier column exists and fill NaN values with empty string
+        if 'multiplier' not in received_df.columns:
+            received_df['multiplier'] = ''
+        else:
+            received_df['multiplier'] = received_df['multiplier'].fillna('')
+            
         global_state.df, global_state.params = received_df.copy(), received_params