It's not that clear cut unfortunately: different devices will react differently depending on whether they are opened for reading or writing. So it might be safe to open "nul" for writing, while reading from it might cause problems. The opposite might be true for another device. To complicate matters, devices may react differently under different versions of Windows.
For the time being, I have added "nul" as an allowed "write" device to /filter.
This is not a good solution because people use NUL in a number of other identifiers, more notably /debug in order to pipe everything to an alias and discard it afterward.
I thought file handling was changed to be consistent all across mIRC. However /debug still seems to be able to use special devices.
//debug -i NUL processRaw
Alias processRaw {
...
}
