public function addPrefix($prefix, $paths)
    {
        if (!$prefix) {
            foreach ((array) $paths as $path) {
                $this->fallbackDirs[] = $path;
            }

            return;
        }
        if (isset($this->prefixes[$prefix])) {
            if (is_array($paths)) {
                $this->prefixes[$prefix] = array_unique(array_merge(
                    $this->prefixes[$prefix],
                    $paths
                ));
            } elseif (!in_array($paths, $this->prefixes[$prefix])) {
                $this->prefixes[$prefix][] = $paths;
            }
        } else {
            $this->prefixes[$prefix] = array_unique((array) $paths);
        }
    }