Stripe_AttachedObject addition to Object.php (lines 146-148) outputs nasty PHP warnings in version 1.9.0

[naomicbush]

After these three lines were added in 1.9.0:

if (self::$_nestedUpdatableAttributes->includes($k))
        $this->_values[$k] = Stripe_Object::scopedConstructFrom('Stripe_AttachedObject', $v, $apiKey);
      else

These warnings are now output on the site when I create a customer, update their subscription, and then retrieve their invoices:

Warning: array_keys() expects parameter 1 to be array, null given in /includes/api/lib/Stripe/Object.php on line 134

Warning: array_diff() [function.array-diff]: Argument #2 is not an array in /includes/api/lib/Stripe/Object.php on line 134

Warning: Invalid argument supplied for foreach() in /includes/api/lib/Stripe/Object.php on line 136

Warning: Invalid argument supplied for foreach() in /includes/api/lib/Stripe/Object.php on line 142

There are no warnings when the three added lines are removed.

May be related to #60