How to detect CNV of normal data using CNVkit

[SF7125]

Hello,
I encountered a problem while running the cnvkit.py batch command for a normal sample in a tumor-only mode. This is the command I used:

cnvkit.py batch ~/CNV/normal_sample.bam -p 12 --fasta ~/CNV/hg19.fa --seq-method wgs --normal --annotate ~/CNV/refFlat.txt --output-dir ~/CNV --scatter --diagram &> ~/CNV/normal_sample.cnvkit.log

I obtained very large copy numbers (e.g., 115) in the CN column of .call.cns output file, which is not logical. Is there anyone who could help clarify why I got this large number as CN in the output?