C#

https://google.github.io/styleguide/jsoncstyleguide.xml[^]

Property names must conform to the following guidelines:

Property names should be meaningful names with defined semantics.
Property names must be camel-cased, ascii strings.
The first character must be a letter, an underscore (_) or a dollar sign ($).
Subsequent characters can be a letter, a digit, an underscore, or a dollar sign.
Reserved JavaScript keywords should be avoided (A list of reserved JavaScript keywords can be found below).

public class IsoDateTimeFormatConverter : IsoDateTimeConverter
{
    public IsoDateTimeFormatConverter(string format)
    {
        DateTimeFormat = format;
    }
}

public class CustomFields
{
    [JsonProperty("post-date")]
    [JsonConverter(typeof(IsoDateTimeFormatConverter), "yyyy-MM-dd")]
    public DateTimeOffset PostDate { get; set; }
}

public class Root
{
    [JsonProperty("custom-fields")]
    public CustomFields CustomFields { get; } = new CustomFields();
}

...

var x = new Root
{
    CustomFields = 
    {
        PostDate = DateTime.Today
    }
};

string json = JsonConvert.SerializeObject(x);
// Output: {"custom-fields":{"post-date":"2019-04-16"}}

public class Root
{
    [JsonProperty("custom-fields")]
    public Dictionary<string, object> CustomFields { get; } = new Dictionary<string, object>();
}

...

var x = new Root
{
    CustomFields = 
    {
        ["post-date"] = DateTime.Today.ToString("yyyy-MM-dd")
    }
};

string json = JsonConvert.SerializeObject(x);
// Output: {"custom-fields":{"post-date":"2019-04-16"}}

Console.WriteLine(JsonConvert.SerializeObject(x));

Gerry Schmitz wrote:

Is Skype a "3rd party"?

Kevin Marois wrote:

I ALWAYS Google first.

List1.clear();
List1.TrimExcess()
List1=null ;


List2.clear();
List2.TrimExcess()
List2=null ;


List3.clear();
List3.TrimExcess()
List3=null ;

GC.Collect();