Do not send a quota guid if no quota is specified.

The runtime has added more checks to prevent bad quotas.  Sending a "" is caught as an invalid quota name.
Sending nothing is the right behavior now.
Can quotas have double quotes in their names? e.g.: `My "scarequote" quota` ?

If so, this code doesn't serialize to JSON properly. Would be nice to clean that up and find the remaining places where we manually smash some strings together to make some JSON.