Enable nullable reference types for generated models

[Copilot]

Collection properties like VolumeMounts are uninitialized by default, causing runtime NullReferenceException when accessed without null checks. The type system provides no indication which properties may be null.

Changes

• Enable nullable context: Added <Nullable>enable</Nullable> to Directory.Build.props

• Update code generator: Modified TypeHelper.cs to emit nullable annotations:

  • Collections: IList<T>? (nullable collection, non-nullable items)
  • Optional properties: string?, V1Lifecycle?
  • Required properties: string Name (non-nullable, per Kubernetes spec)

• Add tests: 5 tests verifying nullable behavior for collections, required properties, and optional properties

Example

Before:

var container = new V1Container();
container.VolumeMounts.Add(new V1VolumeMount()); // Runtime NullReferenceException

After:

var container = new V1Container();
// Compiler warning: VolumeMounts might be null
container.VolumeMounts = new List<V1VolumeMount>
{
    new V1VolumeMount { Name = "vol1", MountPath = "/data" }
};

Developers now receive compile-time warnings for null access, reducing runtime errors and making the API contract explicit.

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Nullables feature request</issue_title>
<issue_description>Could the library start using nullables in the source code? Otherwise its really hard to know what is initialized and what not or you need to check everything.

For example:

var container = new V1Container();
container.VolumeMounts.Add(new V1VolumeMount());

produces:
Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.</issue_description>

Comments on the Issue (you are @copilot in this section)

@tg123 i agree and i am also attempting to migrate everything to `struct`

• Fixes Nullables feature request #1682

---

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