Redirect search block to default Apache Solr search page

For some reason the default search page option on Apache Solr search pages isn’t respected. This form alter hook and submit handler do the trick.

<?php
/**
 * Implements hook_form_FORM_ID_alter().
 */
function my_module_form_search_block_form_alter(&$form, &$form_state) {
  unset($form['#submit']['apachesolr_search_form_search_submit']);
  $form['#submit'][] = 'my_module_search_form_submit';
}

/**
 * Submit callback for search block form.
 *
 * @param $form
 * @param $form_state
 */
function my_module_search_form_submit($form, &$form_state) {
  $search_page = apachesolr_search_page_load(variable_get('apachesolr_search_default_search_page', 'core_search'));
  $form_state['redirect'] = $search_page['search_path'] . '/' . trim($form_state['values']['search_block_form']);
}