Refactor: Simplify parameter validation

Author: onefloid

TM1py/Services/CubeService.py

@@ -145,9 +145,7 @@ def update_or_create_rules(self, cube_name: str, rules: Union[str, Rules], **kwa
         """
         if isinstance(rules, str):
             rules = Rules(rules=rules)
-        if isinstance(rules, Rules):
-            pass
-        else:
+        if not isinstance(rules, Rules):
             raise ValueError('rules must be type str or Rules')
 
         url = format_url("/Cubes('{}')", cube_name)