message: Convenience method for grabbing the default source
diff: @@ -18,6 +18,9 @@ module.exports = class Customer extends Model
  requiresPaymentMethod: ->
  @requiresPayment() and @related().sources.length is 0
  + defaultSource: ->
  + @related().sources.get(@get 'default_source')
  +
  related: ->
  return @__related__ if @__related__?
  