Create empty TiledMapTileLayer?

I want to have optional layers that I don’t have to add to every level in Tiled. If the layer isn’t present in the XML, I would like to initialize it to a blank layer if possible. How do I do this?

Edit: this worked:

try {
    blockExtras = tiledMap.GetLayer<TiledMapTileLayer>("BlockExtras");
} catch {
     blockExtras = new TiledMapTileLayer("BlockExtras", tiledMap.Width, tiledMap.Height, 64, 64);

not quite sure what you are trying to do but I guess the following
tiledMap has a layer and x,y position for each tile, if you want to add special things to each tile just add a list into each tile object, so each one can have extra blocks if needed, and if the list is empty then there is no extra block