TypeError: no implicit conversion of nil into String

https://sentry.gitlab.net/gitlab/gitlabcom/issues/4105352/?referrer=gitlab_plugin

TypeError: no implicit conversion of nil into String
  from ee/lib/gitlab/license_scanning/package_licenses.rb:58:in `join'
  from ee/lib/gitlab/license_scanning/package_licenses.rb:58:in `block in add_records_with_unknown_licenses'
  from ee/lib/gitlab/license_scanning/package_licenses.rb:57:in `each'
  from ee/lib/gitlab/license_scanning/package_licenses.rb:57:in `add_records_with_unknown_licenses'
  from ee/lib/gitlab/license_scanning/package_licenses.rb:48:in `fetch'
  from ee/lib/gitlab/license_scanning/sbom_scanner.rb:16:in `report'
  from ee/app/models/sca/license_compliance.rb:60:in `block in license_scanning_report'
  from lib/gitlab/utils/strong_memoize.rb:34:in `strong_memoize'
  from ee/app/models/sca/license_compliance.rb:59:in `license_scanning_report'
  from ee/app/models/sca/license_compliance.rb:90:in `unclassified_policies'
  from ee/app/models/sca/license_compliance.rb:20:in `block in policies'
  from lib/gitlab/utils/strong_memoize.rb:34:in `strong_memoize'
  from ee/app/models/sca/license_compliance.rb:19:in `policies'
  from ee/app/models/sca/license_compliance.rb:28:in `find_policies'
  from ee/app/controllers/projects/licenses_controller.rb:49:in `matching_policies_from'
  from ee/app/controllers/projects/licenses_controller.rb:24:in `block (2 levels) in index'
...

Further details

https://gitlab.com/gitlab-org/gitlab/-/blob/3b14db78c0a4aed7dfb07638b95ecf683f8b9e4a/ee/lib/gitlab/license_scanning/package_licenses.rb#L58

      def add_records_with_unknown_licenses(records_with_licenses)
        components.each do |component|
          key = File.join(component.name, component.version, component.purl_type)
          next if records_with_licenses[key]

          # return unknown license if the license data for the component wasn't found in the db
          records_with_licenses[key] = Hashie::Mash.new(purl_type: component.purl_type,
            name: component.name, version: component.version, licenses: [UNKNOWN_LICENSE])
        end
      end

add_records_with_unknown_licenses was introduced in !111768 (merged) to address License Scanning reports no license when no pac... (#391294 - closed).

The error occurs comes from the LicenseScanning::SbomScanner, and is trigger when the following conditions are met:

• Some SBOM components don't match any license in the package metadata table.
• component.name, component.version, or component.purl_type is nil.

CycloneDX SBOM can have components that don't have a version.

This is NOT related to the Ruby 3 migration.

Workarounds

• Include the License Scanning CI template in the project CI config.

  include:
  - template: Jobs/License-Scanning.gitlab-ci.yml

• Disable the license_scanning_sbom_scanner for the project when this bug occurs.

  The flag has been enabled on production as part of #385173 (closed).

Possible fixes

Convert nil to "none" so that it can be used as a key.

         key = File.join(component.name || 'none', component.version || 'none', component.purl_type || 'none')