misleading error message from cf-promises

If I accidently have the line
      copy_from    => mycopy("$master_location", "$(source)"),
rather than
      copy_from    => mycopy("$(master_location)", "$(source)"),

in promises.cf,
cf-promises reports:

cfengine>:/var/cfengine/inputs/library.cf:164,0: Broken variable  
syntax or bracket mismatch - inner ($master_location/), near token ''

It would be helpful if the parser reported the correct file, rather  
than pointing to library.cf