Net8.0: DTO Class Settings nullable not applied for FileParameter arguments

[FerdinandStapenhorst]

Version: 14.2.0.0

Even though I enabled the options

• "Generate Nullable Reference Type (NRT) annotations"
  and
• "Generate optional schema properties as nullable properties"

the argument FileParameter is not flagged as nullable.

I have the following Open API example spec:

info:
  title: Test
  version: 1.0.0
openapi: 3.0.3
paths:
  /api/item/{id}:
    patch:
      parameters:
        - $ref: '#/components/parameters/Id'
      requestBody:
        content:
          multipart/form-data:
            schema:
              $ref: '#/components/schemas/UpdateRequest'
        "required": false

      responses:
        '200':
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Item'
          description: updated successfully.

components:
  parameters:
    Id:
      in: path
      name: id
      required: true
      schema:
        type: string
  schemas:
    Item:
      type: object
      properties:
        id:
          type: string  
    UpdateRequest:
      type: object
      properties:
        cover_image:
          format: binary
          type: string
          nullable: true        
        name:
          type: string
          nullable: true
      required: []

The functions signature created looks like this:

public virtual async System.Threading.Tasks.Task<Item> ItemAsync(string id, FileParameter cover_image = null, string? name = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken))

Expected behavior

The functions should have the nullable marker (the question mark) at the FileParameter argument:

public virtual async System.Threading.Tasks.Task<Item> ItemAsync(string id, FileParameter? cover_image, string? name, System.Threading.CancellationToken cancellationToken)

[FerdinandStapenhorst]

The fix looks like this:
In NSwag.CodeGeneration.CSharp.Models.CSharpOperationModel

Just check if the parameter is nullable and add the nullable type annotation (being the question-mark):

       protected override string ResolveParameterType(OpenApiParameter parameter)
        {
            var schema = parameter.ActualSchema;
            var isNullableTypeAnnotation = (!parameter.IsRequired || parameter.IsNullable(_settings.CodeGeneratorSettings.SchemaType)) ?
                "?" : "";

            if (parameter.IsBinaryBodyParameter)
            {
                if (_settings is CSharpControllerGeneratorSettings controllerSettings)
                {
                    if (schema.Type == JsonObjectType.Array && schema.Item.IsBinary)
                    {
                        return controllerSettings.ControllerTarget == CSharpControllerTarget.AspNetCore ?
                            $"System.Collections.Generic.ICollection<Microsoft.AspNetCore.Http.IFormFile{isNullableTypeAnnotation}> " :
                            $"System.Collections.Generic.ICollection<System.Web.HttpPostedFileBase{isNullableTypeAnnotation}>";
                    }
                    else
                    {
                        return controllerSettings.ControllerTarget == CSharpControllerTarget.AspNetCore ?
                            $"Microsoft.AspNetCore.Http.IFormFile{isNullableTypeAnnotation}" :
                            $"System.Web.HttpPostedFileBase{isNullableTypeAnnotation}";
                    }
                }
                else
                {
                    return parameter.HasBinaryBodyWithMultipleMimeTypes ? $"FileParameter{isNullableTypeAnnotation}" : $"System.IO.Stream{isNullableTypeAnnotation}";
                }
            }

            if (schema.Type == JsonObjectType.Array && (schema.Item?.IsBinary ?? false))
            {
                return $"System.Collections.Generic.IEnumerable<FileParameter{isNullableTypeAnnotation}>";
            }

            if (schema.IsBinary)
            {
                if (parameter.CollectionFormat == OpenApiParameterCollectionFormat.Multi && !schema.Type.HasFlag(JsonObjectType.Array))
                {
                    return $"System.Collections.Generic.IEnumerable<FileParameter{isNullableTypeAnnotation}>";
                }

                return $"FileParameter{isNullableTypeAnnotation}";
            }

            return base.ResolveParameterType(parameter)
                .Replace(_settings.CSharpGeneratorSettings.ArrayType + "<", _settings.ParameterArrayType + "<")
                .Replace(_settings.CSharpGeneratorSettings.DictionaryType + "<", _settings.ParameterDictionaryType + "<");
        }