Use nullable reference for AnyType if required

[jacobpovar]

Hi. When using C# code generation from openapi3.0 format and given the following :

• GenerateNullableAnnotations option is enabled,
• and type of nullable object isn't specified:

propertyName:
  type: object
  nullable: true

then Nswag generates code with object type for propertyName, not object?.

Changing AnyType to object? in code generation settings doesn't help either since it results with following code:

public object? PropertyName {get;set;} = new object?();

which can't be compiled.

This PR changes type resolver behavior by append ? to AnyType.

[RicoSuter]

@jeremyVignelles Can you do a review?
It looks good to me.

[RicoSuter]

@jacobpovar Can you also add some tests covering this?

[jeremyVignelles]

Does the code still generate = new object(); ?

I don't think it's the right thing to return(should be null), but that would likely break things to change it now.

If there is = new object();, can it still be null or will it just be skipped by deserialization?
If it can't be null, there's no point of making the type nullable

[jacobpovar]

@RicoSuter @jeremyVignelles thank you for reviewing this request

@RicoSuter sure, added couple of tests.

@jeremyVignelles

An object will have new object() initializer only if it's required.
when reading jsonschema from C# class then both optional and required fields will have = default! initializer.

when reading schema from json (the difference is that properties have explicit object type now) an optional field still has = default! initializer and will remain null.
a required field will have new object() initializer as it had before my changes.

So, if I'm not mistaken, If property is not set, it will remain null after deserialization. If it's present, then it won't be null.

[jeremyVignelles]

I didn't check but that sounds good 🙂 Thanks for the explanations