public function coreCreate($core, $instancedir, $config = null, $schema = null, $datadir = null)
    {
        $args = array('instanceDir' => $instancedir);
        if ($config) {
            $args['config'] = $config;
        }
        if ($schema) {
            $args['schema'] = $schema;
        }
        if ($datadir) {
            $args['dataDir'] = $datadir;
        }

        return $this->coreCommand('CREATE', $core, $args);
    }