Hi Izaias,
Currently users can specify whether or not to match records if both fields or either field is blank or if blank values should be disregarded entirely from the process.
If that options are not enough you can easily replicate desired custom logic using custom Transform in the preprocessing setting. Feel free to reach out to support for help.
Izaias Neto
Currently you can either match exactly and allow blank values to match or match exactly and do not allow blank values to match. However, it would also be useful if blacks did match, but only with other blanks.