public function getPHPIncludeFolders()
    {
        if (!is_array($this->framework_folders)) {
            $this->framework_folders = array();

            if (is_dir(NABU_SRC_PATH)) {
                $this->framework_folders[] = realpath(NABU_SRC_PATH);
            }
            if (is_dir(NABU_SDK_PATH)) {
                $this->framework_folders[] = realpath(NABU_SDK_PATH);
            }
            if (is_dir(NABU_PUB_PATH)) {
                $this->framework_folders[] = realpath(NABU_PUB_PATH);
            }
            if (is_dir(NABU_LIB_PATH)) {
                $this->framework_folders[] = realpath(NABU_LIB_PATH);
            }
            if (is_dir(NABU_ICONTACT_PATH)) {
                $this->framework_folders[] = realpath(NABU_ICONTACT_PATH);
            }
            if (count($this->framework_folders) === 0) {
                $this->framework_folders = null;
            }
        }

        return $this->framework_folders;
    }