When I saw the change, I felt at first that [—no value—] was better than [none].
Then I noticed that [none] was a better answer when I asked myself “what is that card’s dimension value again?”, but with certain dimension labels only.
In conclusion, I feel it is the “—” that conveys the best the idea of an empty dimension, whatever the word in the middle.
NB: I have actually already created a [I’m not decided yet] value for certain dimensions where I needed to pin on it my undecided thought.