OpenApiParameter.Explode is not serialized correctly for Query parameters.

[bingnz]

I'm stealing this bug report from domaindrivendev/Swashbuckle.AspNetCore#1212, as NSwag has the same issue.

As per the openapi parameter specification for Query Parameters, when the style is set to form, the default explode value is true.

When adding a parameter like so:

OpenApiParameter param = new OpenApiParameter();
param.name = "Foo";
param.In = ParameterLocation.Query;
param.Style = ParameterStyle.Form;
param.Explode = false;
param.Schema = new OpenApiSchema
{
    Type = "array",
    Items = new OpenApiSchema
    {
        Type = "string"
     }
};

This serializes to:

"parameters": [
{
  "name": "Foo",
  "in": "query",
  "style": "form",
  "schema": {
    "type": "array",
    "items": {
      "type": "string"
    },
  }
}]

The explode property is not serialized because it has [JsonProperty(DefaultValueHandling = DefaultValueHandling.Ignore, PropertyName = "explode")] applied and false is the default value in C#. Because false is the default value, it's never serialized to JSON.
I can work around this by creating a custom OpenApiParameter derived class that has its own JsonPropertyAttribute to serialize the value - but this only works at runtime and not when generating the spec using nswag.exe. I'm not sure why that is, but I suspect the command line tool deserializes the generated spec and re-serializes it, and when it does so it doesn't have my overridden OpenApiParameter.

[bingnz]

I believe this may be addressed by #2961.