Equivalent to nullptr

[Leonardo via Digitalmars-d-learn]

I was trying to use Derelict-SDL2 library, and the tutorial do 
this code below, as C++ code has nullptr word. How I use this?

---------------------------------
struct Ball
{
  SDL_Rect bbox = {0, 0, 100, 100};
  SDL_Point vel = {1, 1};
}
---------------------------------
case SDL_MOUSEBUTTONDOWN:
{
  SDL_Point mousePos = {event.button.x, event.button.y};
  if(event.button.button == SDL_BUTTON_LEFT && 
SDL_EnclosePoints(&mousePos, 1, &ball.bbox, nullptr) )
  {
    SDL_Log("CLICK");
    if(abs(ball.vel.x) < 32)
    {
      ball.vel.x *= 2;
      ball.vel.y *= 2;
    }
  }
  break;
}