[mwawacek]

PR Checklist

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

A circuit breaker, bulkhead or backoff field that a preset (or ResilienceService.create()) sets to undefined replaces the module default instead of inheriting it. ConfigService.get() gives undefined for a setting that isn't set:

ResilienceModule.forRootAsync({
  inject: [ConfigService],
  useFactory: (config: ConfigService) => ({
    defaults: { circuitBreaker: { minimumCalls: 1 }, bulkhead: { maxConcurrent: 2 } },
    presets: {
      carrier: {
        circuitBreaker: { minimumCalls: config.get<number>('CARRIER_MIN_CALLS') }, // undefined
        bulkhead: { maxConcurrent: config.get<number>('CARRIER_MAX_CONCURRENT') }, // undefined
      },
    },
  }),
});

resilience.circuitBreaker('carrier').options.minimumCalls; // 10 (built-in), expected 1
resilience.bulkhead('carrier').maxConcurrent;              // 10 (built-in), expected 2

The same happens to retry.backoff fields (backoff: { delay: undefined } drops defaults.retry.backoff.delay). Top-level retry options and decorator options already skip undefined fields (definedFields()). (A value parsed from an unset variable, such as Number(process.env.X), is NaN instead, which already fails the boot naming the option.)

Issue Number: N/A

What is the new behavior?

undefined fields are dropped before circuit breaker, bulkhead and backoff options are merged over the module defaults, as they already are for retry options. definedFields() moves to utils/options.util.ts so the registries can use it without importing PolicyFactory.

Does this PR introduce a breaking change?

• Yes
• No

Other information

A field set to undefined now always inherits. So bulkhead: { queueTimeout: undefined } in a preset no longer removes a defaults.bulkhead.queueTimeout; there is no other value for "no limit" there (Infinity is rejected as a duration).