Response validation incorrectly fails for undefined values for additionalProperties

[ghost91-]

Describe the bug
When using a schema that has additionalProperties set to some type, and when then returning an object that has an additional property set to undefined, the response validation fails. Instead, it should ignore the undefined values, because they will be filtered out when serializing the response to JSON.

To Reproduce
Steps to reproduce the behavior.

• Create an OpenAPI spec that has some response with

  additionalProperties:
    type: string

• Activate response validation
• Return an object that has an additional property set to undefined

Actual behavior
undefined values make validation of additionalProperties fail

Expected behavior
undefined values are ignored for validation additionalProperties in response validation