Create set of false positives or ngatives for inputs with empty truth sets.

def _setup_call_false(vrn_file, rm_bed, base_dir, data, call_type):
    """Create set of false positives or ngatives for inputs with empty truth sets.
    """
    out_file = os.path.join(base_dir, "%s.vcf.gz" % call_type)
    if not utils.file_exists(out_file):
        with file_transaction(data, out_file) as tx_out_file:
            if not vrn_file.endswith(".gz"):
                vrn_file = vcfutils.bgzip_and_index(vrn_file, out_dir=os.path.dirname(tx_out_file))
            cmd = ("bcftools view -R {rm_bed} -f 'PASS,.' {vrn_file} -O z -o {tx_out_file}")
            do.run(cmd.format(**locals()), "Prepare %s with empty reference" % call_type, data)
    return {call_type: out_file}