chore: return None instead of -1

Author: datitran

priceloopcurrency/function.py

@@ -5,7 +5,7 @@ def return_currency_rates(from_currency: str, to_currency: str) -> float:
   try:
     return str(c.get_rate(from_currency, to_currency))
   except:
-    return str(-1)
+    return None
 
 def handler(event, context):
   return list(map(lambda row: return_currency_rates(row[0], row[1]), event["BatchedArgs"]))