Created by: mickroll

Fixes #9654

For required attributes, generate @NotNull only, if attribute is neither readOnly nor writeOnly. This reflects the spec https://swagger.io/docs/specification/data-models/data-types/#readonly-writeonly

If a readOnly or writeOnly property is included in the required list, required affects just the relevant scope – responses only or requests only. That is, read-only required properties apply to responses only, and write-only required properties – to requests only.

Using @NotNull for these cases would fail validation in the other direction, where the attribute is intentionally not present.

@nmuesch

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