Although seven were counted as having voted "no" only six names were recorded. This is, apparently, not unusual!
My understanding is that it is because to force a vote, an Opposition MP had to declare that they were opposed to the motion (to stop it being nodded through, and that MP is then included in the number of Nos (and I think does not actually vote)
Obviously, the opposition parties would want a vote on this because those who are abstained can easily (and correctly, imo) be targeted in future election as opposed to Parliamentary sovereignty, cowardly, anti-democracy, pro-Johnson, unprincipled, etc etc etc