I'd generate a blank line using
vaProxy.WriteToLog("");
rather than
vaProxy.WriteToLog(null);
In my case, at least, null would be the result of something like
vaProxy.WriteToLog(vaProxy.GetText(valueThatIsn'tSet));
in which case knowing whether the value was null can be useful, as otherwise it'd be impossible to distinguish between "" and null/"Not Set" without additional handling.