private function fillMissing($data, $existingData = []) {
	if($this->isAssoc($data)) {
		foreach ($this->headers as $header) {
			if(!isset($data[$header])) {
				$replaceWith = isset($existingData[$header])
					? $existingData[$header]
					: "";
				$data[$header] = $replaceWith;
			}
		}
	}
	else {
		end($this->headers);
		for($i = 0, $max = key($this->headers); $i <= $max; $i++) {
			if(!isset($data[$i])) {
				$replaceWith = isset($existingData[$i])
					? $existingData[$i]
					: "";
				$data[$i] = $replaceWith;
			}
		}
		ksort($data);
	}

	return $data;
}