Please help me to understand why AV is going on here (http://pastebin.com/YkAqQ604):

Please help me to understand why AV is going on here (http://pastebin.com/YkAqQ604):

program Project1;

{$APPTYPE CONSOLE}
{$R *.res}

uses
  System.SysUtils, System.Classes, System.JSON, Data.DBXJSONReflect;

function Marshal(AObject: TObject): string;
var
  Marshaller: TJSONMarshal;
begin
  Marshaller := TJSONMarshal.Create;
  try
    Result := Marshaller.Marshal(AObject).ToJSON;
  finally
    FreeAndNil(Marshaller);
  end;
end;

function Unmarshal(AString: string): TStringList;
var
  Unmarshaller: TJSONUnMarshal;
  JV: TJSONValue;
begin
  Unmarshaller := TJSONUnMarshal.Create;
  try
    JV := TJSONObject.ParseJSONValue(AString);
    try
      Result := Unmarshaller.Unmarshal(JV) as TStringList;
    finally
      FreeAndNil(JV);
    end;
  finally
    FreeAndNil(Unmarshaller);
  end;
end;

function MarshalUnmarshal: string;
var
  StringList: TStringList;
  Marshaled: string;
begin
  StringList := TStringList.Create;
  try
    StringList.Text := 'abc';
    Marshaled := Marshal(StringList);
  finally
    FreeAndNil(StringList);
  end;

  StringList := Unmarshal(Marshaled);
  try
    Result := StringList.Text;
  finally
    FreeAndNil(StringList);
  end;
end;

begin
  try
    Writeln(MarshalUnmarshal);
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;

end.
http://pastebin.com/YkAqQ604