prevent emty class attribute added to each cell ( class=" " )

Dear supporters,
i'm trying to clean up a large data table as much as possible to improve loading and processing performance.
besides the usual optimizations, i also try to clean up the source DOM as much as possible, that is removing unneeded classes etc.
after i have removed almost all classes, i see that datatables adds an emty class attribute to each cell.

So my original DOM is: <td>foo</td>
and datatables processes and creates: <td class=" ">foo</td>

I'm wondering if this is any purpose, and if not, if i could prevent doing it, as i think adding lets say 1000x20 attributes to the DOM may take some time in slower browsers ...

I have searched the documentation, but could not find anything about cell classes, only about row classes so far.

thanks for your help
hirnsaege