strange issue when using difference in 3.0

[jamesdixon]

Hi,
I have a model that has a property which uses the difference macro to, obviously, get the difference between two of the model's properties. Here it is:

import Model from 'ember-data/model';
import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';
import EmberCPM from 'ember-cpm';
const { Macros: { difference } } = EmberCPM;

export default Model.extend({
  business: belongsTo(),
  invoices: hasMany(),

  payments: attr('number'),
  totalBilled: attr('number'),
  unpaid: difference('totalBilled', 'payments')
});

Strangely, I'm getting a NaN for the unpaid property when totalBilled = 15 and payments = 0. Digging into the macro itself, I'm seeing that firstNumber is properly set to 15, but secondNumber is actually the name of the property, payments, rather than 0. Odd, right?

If I downgrade to v2.1.3 of ember-cpm, everything works as expected.

I'm running Ember 2.11.3.

Thanks in advance for any help!