TJsonObjectBuilder wirft Exception

[Der schöne Günther]

Ganz unkompliziert gefragt: Was mache ich falsch?

Delphi-Quellcode:

uses System.Json.Builders, System.Json.Writers;

procedure p();
var
   writer: TJsonWriter;
   builder: TJSONObjectBuilder;
begin
   writer := nil; builder := nil;
   try
      writer := TJsonObjectWriter.Create(True);
      builder := TJSONObjectBuilder.Create(writer);

      builder.Clear();
         // Exception: EJSONCollectionBuilderError
         // This operation is not permitted without assigned callback
   finally
      builder.Free(); writer.Free();
   end;
end;