Partial updates and explicit null

PATCH endpoints must distinguish three states for nullable fields: omitted, a concrete value, and explicit JSON null.

The SDK request objects track whether a nullable property's initializer ran.

var unchanged = new UpdateDocumentRequest();

This request omits caption completely.

var clearCaption = new UpdateDocumentRequest
{
    Caption = null
};

This request sends:

{
  "caption": null
}

The same behavior applies to nullable PATCH fields such as project description, board color/WIP limit, ticket description/due date, and document project/caption/content.

Optional non-nullable fields use nullable C# wrappers such as bool? or enum nullable values. A null wrapper means "do not send this property" because the OpenAPI schema does not allow JSON null for those fields.

This design prevents an empty update object from clearing fields accidentally and preserves server-side defaults during create operations.