How to represent a null string field using ObjectToJSON in mORMot?

I'm using the mORMot framework in FreePascal to serialize objects into JSON. I need one of the string fields to be represented as null in the generated JSON, instead of an empty string. However, when using the ObjectToJSON function, the field appears as an empty string.

Here's an example of what I'm trying to do with a class:

uses
  SysUtils,
  SynCommons;

type
  TPersonClass = class(TSynPersistent)
  private
    FName: String;
    FAge: Integer;
  published
    property Name: String read FName write FName;
    property Age: Integer read FAge write FAge;
  end;

var
  Person: TPersonClass;
  JSON: RawUTF8;
begin
  Person := TPersonClass.Create;
  try
    Person.Name := ''; // I want this to be null in the JSON
    Person.Age := 30;
    
    JSON := ObjectToJSON(Person, [woHumanReadable]);
    Writeln(JSON);
  finally
    Person.Free;
  end;
end.

The current output is something like:

{
  "Name": "",
  "Age": 30
}

But I would like the JSON to be:

{
  "Name": null,
  "Age": 30
}

How can I adjust the serialization so that the Name field is null instead of an empty string? Is there any configuration or best practice in mORMot for handling this?

I find the solution! To represent a null string field in JSON using mORMot, you can declare the property as a Variant type. This allows you to explicitly assign Null to the field when you want it to be null in the JSON output.

type
TPersonClass = class(TSynPersistent)
  private
    FAge: Integer;
    FName: Variant;
  published
    property Name: Variant read FName write FName;
    property Age: Integer read FAge write FAge;
  end;

And you can use it like this:

var
 Person: TPersonClass;
  JSON: RawUTF8;
begin
  Person := TPersonClass.Create;
  try
    
    Person.Name := Null; // This will be serialized as null
    //Person.Name := 'Jhon';// Output: { "Name": "Jhon", "Age": 30 }
    Person.Age := 30;
    
    JSON := ObjectToJSON(Person, []);
    Writeln(JSON); // Output: { "Name": null, "Age": 30 }
  finally
    Person.Free;
  end;
end.