we write this error even if extract-conclusion-params from the builder type fails, and it fails if
one argument is a Pack on a subject other than the current subject, since the code of copy-pack-holes only works if there is a Pack on the subject (it should not fails but succeed doing nothing
@pi8027 has an example where a legitimate builder has a parameter that is a Pack on a constant (and its class), I don't know why
extract-conclusion-paramsfrom the builder type fails, and it fails ifcopy-pack-holesonly works if there is a Pack on the subject (it should not fails but succeed doing nothing