src/Helper/MimeType.php
public static function getExtensionFor(string $mimetype): ?string
    {
        $extensions = static::getExtensions();
        if (false !== $match = array_search($mimetype, $extensions, true)) {
            return $match;
        }

        return null;
    }
public static function getExtensionFor(string $mimetype): ?string
    {
        $extensions = static::getExtensions();
        if (false !== $match = array_search($mimetype, $extensions, true)) {
            return $match;
        }

        return null;
    }
fetch file-extension for given mimetype
@param  string $mimetype
@return string|null