[Dgame] Sprite loading and setting position in another class

[Jack via Digitalmars-d-learn]

So I've been using Dgame to learn about game development and I'm 
having an error when I'm trying to set a sprite's position 
initialized and stored in another class.

Basically my code is:
//Texman.d//////////////////////////////////////
Class Texman
{
  //variables

        void addSprite(string sprite_file, string name)
        {
                Surface wiki_img = Surface(sprite_file);
                Texture wiki_tex = Texture(wiki_img);
                sprite_list[name] = new Sprite(wiki_tex);
                sprite_list[name].setPosition(1,1); //tried to 
remedy by this		
        }
}

//GameObject.d////////////////////////////

class GameObject
{
Sprite sprite;
float location_x;
float location_y;
//other variables

        void setLocation(float x, float y)
        {
                sprite.setPosition(x,y);
                location_x = x;
                location_y = y;
        }
}

//main.d/////////////////////////////////


        void create()
        {
                wnd = Window(1024, 720, "Dgame Test");
                sample_object = new GameObject();
                texman = new TextureManager();
                texman.addSprite("images.png", "kirino");
                sample_object.setSprite(texman.getSprite("kirino"));
                sample_object.setLocation(500,500);
        }
//////////////////////////////////////////////////////

And I'm having an error namely
"First-chance exception: core.exception.AssertError null"
pointing at the setLocation on GameObject.d.

I tried to remove the "setLocation" method and tried to set 
Location on TextureManager itself and it worked.

So is setting the position of a sprite outside of the class it 
initialized into forbidden, or am I doing something wrong here?