Milestone calculation fails in a certain condition

Milestone calculation fails if we have non-XX.YY in milestones.

https://gitlab.com/gitlab-org/gitlab-feature-flag-alert/-/blob/91a295185210683d2e17896211797bf874127ee4/lib/gitlab/feature_flag_alert/milestone.rb#L12-18

      def ago(num_milestones)
        major, minor = value.split(".").map(&:to_i)

        older_major = minor > 1 ? major : major - 1
        older_minor = (0..12).to_a[minor - num_milestones]

        [older_major, older_minor].join(".")

Execution log

$ bundle exec bin/feature-flag-alert
Cloning into 'gitlab-repo'...
Updating files: 100% (53018/53018), done.
bundler: failed to load command: bin/feature-flag-alert (bin/feature-flag-alert)
NoMethodError: undefined method `>' for nil:NilClass
  /builds/gitlab-org/gitlab-feature-flag-alert/lib/gitlab/feature_flag_alert/milestone.rb:15:in `ago'
  /builds/gitlab-org/gitlab-feature-flag-alert/lib/gitlab/feature_flag_alert/monitor.rb:22:in `run'
  bin/feature-flag-alert:6:in `<top (required)>'
Current milestone: ClickHouse Acceleration

from https://gitlab.com/gitlab-org/gitlab-feature-flag-alert/-/jobs/2546090764

Blocks !15 (merged)