PHP Notice: Undefined property: stdClass::$settings in feeds_tamper.module on line 67.

Steps to reproduce:

1. Create a new Drupal installation with Feeds, Feeds Tamper, and dependencies.
2. Create a node importer (CSV), with a title field.
3. Make the title field required w/ Feeds Tamper.
4. Import a CSV.

The "Required Field" plugin does not have any settings, line 67 of feeds_tamper.module (as well as lines 60 and 64) assumes that the settings piece will be there:

<?php
          if ($is_array && $plugin['multi'] == 'loop') {
            foreach ($item[$element_key] as &$i) {
              $plugin['callback']($source, $item_key, $element_key, $i, $instance->settings);
            }
          }
          elseif ($is_array && $plugin['multi'] == 'direct') {
            $plugin['callback']($source, $item_key, $element_key, $item[$element_key], $instance->settings);
          }
          elseif (!$is_array && $plugin['single'] != 'skip') {
            $plugin['callback']($source, $item_key, $element_key, $item[$element_key], $instance->settings);
          }
?>