Filtering rows containing NaN's

I am using SlickGrid (via qgrid) for filling manually missing data in my frames. (typing in grades for students actually!). For this application, it would be helpful to be able to filter rows containing NaNs, whereas, in typical use cases, those are the rows to be filtered out. Could this feature be added to SlickGrid? Typically by (optionally) displaying NaN in the list of values to be selected in the filter setup UI?

Thanks in advance, Nicolas