public static Spatial getPlaceholderModel(AssetManager assetManager){
        // What should be the size? Nobody knows
        // the user's expected scale...
        Box box = new Box(1, 1, 1);
        Geometry geom = new Geometry("placeholder", box);
        Material mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
        Texture tex = assetManager.loadTexture("Common/Textures/MissingModel.png");
        tex.setWrap(Texture.WrapMode.Repeat);
        mat.setTexture("ColorMap", tex);
        geom.setMaterial(mat);
        return geom;
    }
A private constructor to inhibit instantiation of this class.
jme3-core/src/main/java/com/jme3/util/PlaceholderAssets.java