$field->options['group_enabled'] throws undefined index in PHP 5.5.9

After updating to PHP 5.5.9 I get the following error using apache solr views.

Notice: Undefined index: group_enabled in apachesolr_views_query->get_group_info() (line 41 of  sites/all/modules/contrib/apachesolr_views/apachesolr_views_query.inc).

After having a look the cause is a conditional check that when a group isn't defined, is throwing the error. To fix, the method just needs to be update to be:

/**
 * Build our grouping information for the query.
 */
public function get_group_info($field) {
  if (isset($field->options['group_enabled']) && $field->options['group_enabled'] == 'yes') {
    $this->grouping_info['group'] = TRUE;
 
    if (isset($this->grouping_info['groups'][$field->options['group_id']])) {
      $this->grouping_info['groups'][$field->options['group_id']] .= ',' . $field->field_alias;
    }
    else {
      $this->grouping_info['groups'][$field->options['group_id']] = $field->field_alias;
    }
  }
}

Happy to provide a patch for this one if you want it fixed and it already isn't addressed in the dev version already.