refactor: Strict null checks (#13342)

lib/datasource/metadata.spec.ts

lib/datasource/metadata.ts

lib/manager/gradle/shallow/utils.ts

lib/manager/helm-values/util.ts

lib/manager/npm/post-update/rules.ts

lib/manager/pre-commit/parsing.ts

lib/versioning/ruby/version.ts

tsconfig.strict.json