Some airports don't measure, or don't report Braking Action. For instance, Narita.
I once taxied out there in a tropical storm - torrential rain was falling and it was blowing a gale. 25kt mean crosswind. The ramps and taxiways were flooded.
I asked ATC for a Braking Action Report and was told 'Not measured or available'.
So what do you do?
Assume the BA is 'Good' and just plough on?
Or assume it's Medium and in fact outside limits - then what?
Or assume its really what it looks like - Poor - and taxi back in?
I'd take a PIREP. In the circumstances its your only option.