If the value is an enumeration you could use that in the split. So if grade contains an enum Medal with the values Gold, Bronze, Silver and empty put $Grade/Medal inside the split. Or if you do not have an enum create a variable with that enum and use if statements to fill it like if $Grade/someValue =>0 and $Grade/someValue <=33 then yourmodulename.Medal.Bronze else ….
Otherwise use multiple splits as Jeremie told you.
Use multiple decision.