JOSM Validator: Cannot add MapCss rule: Cannot add instruction fixremove

I have this JOSM validator mapcss-rule below, which works fine.

*[ADDRESS] {
  throwerror: tr("{0} should not be uploaded", "{0.key}");
  group: tr("no-import tag");
  /* fixremove: "{0}"; */
}

If I try to uncomment the line with fixremove JOSM gives me this message in the terminal

SEVERE: Cannot add MapCss rule: Cannot add instruction fixremove: {0}!

And this is the same for any value of "fixremove" or "fixadd" I try.

What is the problem here? What do I have to do to get this working?