Angular Typescript: Swagger CodeGen Generator making all class properties Nullable

We are auto generating proxies with SwaggerCodeGen https://swagger.io/ .

This will reduce manually typing in hundreds of classes. We noticed all model class properties are Nullable ? in SwaggerCodeGen.

When they wrote this, doesn’t it break the interface contract when some members as required?
What is the reason SwaggerCodeGen did this? In our same C# corresponding class, they are not nullable.

export interface Product{ 
    productId?: number;
    productName?: string;
    productType?: number;
    manufacturer?: string;
    inventory?: number;

Currently converting C# classes to Angular Typescript 10.

Another topic:

Similarly in NSwag Studio,

They are doing this with Union Types undefined, instead of nullable. Is this the same thing as Swagger CodeGen,

export interface Product {
    productId: number | undefined;
    productName?: string | undefined;
    productType?: number | undefined;
    manufacturer?: string | undefined;
    inventory?: number | undefined;

definitions:
  Order:
    required:
      - id
      - petId
    properties:
      id:
        required: true
        type: integer
        format: int64
      petId:
        type: integer
        format: int64
      quantity:
        required: true
        type: integer
        format: int32