Eliminate unnecessary use of missing_data

Author: todd

sysdata/futures/instruments.py

@@ -42,8 +42,9 @@ def update_slippage_costs(self, instrument_code: str, new_slippage: float):
     def upate_meta_data(self, instrument_code: str, meta_name: str, new_value):
         instrument_object = self.get_instrument_data(instrument_code)
         existing_meta_data = instrument_object.meta_data
-        existing_meta_data_value = getattr(existing_meta_data, meta_name, missing_data)
-        if existing_meta_data_value is missing_data:
+        try:
+            existing_meta_data_value = getattr(existing_meta_data, meta_name)
+        except AttributeError:
             raise Exception(
                 "Meta data %s does not exist for instrument %s"
                 % (meta_name, instrument_code)