GlFilteredSearch: error in example when using "Confidential" filter

Noticed this error when using the GlFilteredSearch example:

Steps to reproduce

1. Go to https://gitlab-org.gitlab.io/gitlab-ui/?path=/story/base-filtered-search--default
2. Clear out the filtered search
3. Choose "Confidential"
4. Choose "=" or "!="
5. Choose "Yes" or "No"