The OpenAPI spec: ``` "TestEntityDto": { "type": "object", "properties": { "id": { "type": "string", "format": "uuid" }, "name": { "type": "string", "nullable": true }, "created": { "type": "string", "format": "date-time" }, "lastModified": { "type": "string", "format": "date-time" } }, "additionalProperties": false }, ``` The generated type: ``` export type TestEntityDto = { id?: string; name?: string | null; created?: string; lastModified?: string; }; ``` Why is the `id` nullable?