Base::convertArrayKeysToUpper

protected function convertArrayKeysToUpper(array $array, $levels = 0, $currentLevel = 0)
{
	$result = [];
	foreach($array as $key => $value)
	{
		if($levels > 0 && is_array($value) && $currentLevel < $levels)
		{
			$currentLevel++;
			$value = $this->convertArrayKeysToUpper($value, $levels, $currentLevel);
			$currentLevel--;
		}
		$result[$this->toUpperCase($key)] = $value;
	}

	return $result;
}