calling deleteByQuery causes error: "Call to a member function deleteByQuery() on a non-object"

If deleteByQuery is called (and apachesolr is not fully configured), it causes a PHP error: Call to a member function deleteByQuery() on a non-object in /.../apachesolr/apachesolr.admin.inc on line 448.

This is because it assumes apachesolr_get_solr() will always succeed.

function apachesolr_delete_index($type = NULL) {
  // Instantiate a new Solr object.
  $solr = apachesolr_get_solr();
  if ($type) {
    $query = 'type:' . $type;
  }
  else {
    $query = '*:*';
  }
  // Allow other modules to modify the delete query.
  // For example, use the site hash so that you only delete this site's
  // content:  $query = 'hash:' . apachesolr_site_hash()
  drupal_alter('apachesolr_delete_index', $query);
  $solr->deleteByQuery($query);

apachesolr_get_solr() fails gracefully, so we can wrap all this in an if clause:

function apachesolr_delete_index($type = NULL) {
  // Instantiate a new Solr object.
  if ($solr = apachesolr_get_solr()) {
    if ($type) {
      $query = 'type:' . $type;
    }
    else {
      $query = '*:*';
    }
    // Allow other modules to modify the delete query.
    // For example, use the site hash so that you only delete this site's
    // content:  $query = 'hash:' . apachesolr_site_hash()
    drupal_alter('apachesolr_delete_index', $query);
    $solr->deleteByQuery($query);

This allows third-party modules to call deleteByQuery without having to check that apachesolr is properly configured.
Patch attached.