InvalidCastException: Value is not a convertible object

hey guys, i try to check if a config is existing or not.
i tried:

Code:

string UserName = hitInfo?.Initiator?.ToPlayer().displayName;
if (!(bool)Config.Get("Dmg", UserName))

but that gives me "InvalidCastException: Value is not a convertible object"

anybody a idea how to solve this problem?

thank you