CSV error when using parameters with --reference

This bug manifests when using --parameter-scan and --reference together, e.g.

hyperfine \
  --runs 1 \
  --reference "sleep 1" \
  --parameter-scan secs 2 3 \
  --export-csv out.csv 'sleep {secs}'

The first parameterised run after the reference gives the following error when complete:

Error: CSV error: found record with 9 fields, but the previous record has 8 fields

Looking at out.csv, I can see that the column name for the secs parameter is missing:

command,mean,stddev,median,user,system,min,max
sleep 1,1.00279931462,0,1.00279931462,0.0006699600000000003,0.0018847000000000004,1.00279931462,1.00279931462

I would expect the parameter columns to exist but their values for the reference run to all be missing, since there is doesn't seem to be a way to specify what their values are in the reference command.