private function _checkLayerConfig()
    {
        $errorString = array();
        if ($this->_providerID == '') {
            array_push($errorString, 'LAYER_PROVIDER_ID');
        }

        if ($this->_keyID == '') {
            array_push($errorString, 'LAYER_PRIVATE_KEY_ID');
        }

        if ($this->_privateKey == '') {
            array_push($errorString, 'LAYER_PRIVATE_KEY');
        }

        if (count($errorString) > 0) {
            $joined = implode(',', $errorString);
            trigger_error("$joined  not configured. See README.md", E_USER_ERROR);
        }
    }