TaskQuery::prepareGroupBy

private function prepareGroupBy($groupBy): array
{
	if (is_string($groupBy))
	{
		$groupBy = [$groupBy];
	}

	if (!is_array($groupBy))
	{
		throw new InvalidGroupByException();
	}

	foreach ($groupBy as $column)
	{
		if (!is_string($column))
		{
			throw new InvalidGroupByException();
		}
	}

	return $groupBy;
}