function getEmptyLineNums(lines) {
	const emptyLines = lines
		.map((line, i) => ({
			code: line.trim(),
			num: i + 1,
		}))
		.filter(line => !line.code)
		.map(line => line.num);

	return emptyLines;
}
Return an array with any line numbers that are empty.
@param {Array} lines An array of each line of the file.
@returns {Array} An array of line numbers.