Value overwritten with null on update API call when field has unique name

When an API call is made to an entity which has a field with a unique name, but that field is not included in the API parameters, array, _civicrm_api3_swap_out_aliases will create that parameter with a null value. On update calls, the preexisting value will be overwritten with null. The unit test api_v3_PledgePaymentTest::testUpdatePledgePayment fails because of that.

This is the offending line (_civicrm_api3_swap_out_aliases, api/v3/utils.php line 1037):

}elseif(empty($apiRequest['params'][$field]) && CRM_Utils_Array::value('uniqueName', $values) && $field != $values['uniqueName'])

{ $apiRequest['params'][$field] = CRM_Utils_Array::value($values['uniqueName'],$apiRequest['params']); }

The attached patch adds an array_key_exists check. It should probably done for the other two if branches too, but I wasn't sure about that.