After reading the questions and comments, I would suggest doing any of the following:
Create an robots.txt with only one line in it. Maybe something like this:
# it works
Or if you don't really want a robots.txt file, then configure your server so that all requests to robots.txt result in an HTTP 410 status code, meaning the file is gone and it should not be requested ever again.
If your server is apache, you can easily add the following contents to .htaccess in the document root folder of your site, or inside the directory tags where the directory is the document root in the main server configuration.
RewriteRule ^robots\.txt$ - [R=410,NC,L]
This will cause any request to robots.txt (regardless of letter casing) to produce an HTTP 410 status code.
I added a forward slash before the dot in the file name to make the dot a literal character instead of a rule-processing character.
The advantage to having a plain robots.txt file as opposed to no robots.txt file is that your error logs won't be filled up with requests to robots.txt.