There is no such official command as
robots.txt. By default, everything is allowed. (However, it is possible to use
Allow to give exceptions when you are disallowing many directory paths in one route. Often, there is no requirement for this though).
Not that I would expect it to cause an issue however.
There is no reason to specify the Mediapartners-Google user agent either as this too, is just saying allow the crawling of everything.
robots.txt needs from the above is the following:-
Google Webmaster Tools will report a warning to say X amount of URL's on your site were blocked by your
robots.txt if you are disallowing bots to any part of your site, in which case you are at
/search/. You can expand this notice to view specifically what URL's were blocked and you may well find that it is only the ones you want disallowed that Google Webmaster Tools is warning about.
You can also run an application such as Xenu to crawl your site and establish what URL's can be crawled specifically. You can also fetch as Googlebot and test your
robots.txt file from within Google Webmaster Tools that will alert you to any further issues or at least complete details of any issues.
Upon further clarification, added
Disallow directive for UA Mediapartners-Google.