How to generate an accessible empty string in alt tag?

Sitefinity's default is to automatically generate the alt tag from the file name of the image. However, most of the images we have on our site are decorative, and proper alt tag usage means we should have an empty string, so screen readers won't announce them. 

But when I delete the contents of the alt tag for the image, the source code generated on the page where the image is located comes up with alt, not alt="" which is the proper usage. When I go back and insert a space in the alt text field, the result is alt=" " in the code, which is better than originally (I guess), but still not proper usage. If there is a space between the double quotes, screen readers still might announce it.

I am working on a site in the public sector, and would like to do accessibility correctly. Is there a way in the user-facing Sitefinity system to generate a proper alt="" tag? Thanks!