GridServiceForm::getIndexFieldDescription

private function getIndexFieldDescription(array $description, string $key, string $fieldName): ?int
{
	$result = null;

	foreach (array_keys($description) as $index)
	{
		if ($description[$index][$key] === $fieldName)
		{
			$result = $index;
			break;
		}
	}

	return $result;
}