ShapedRecipe setIngredient

Hey, i want do set an Ingredient by an MaterialData, but ingame it is only Air...

public RecipeManager() {
plugin = Main.getPlugin();

ItemStack backpacksmall = new ItemStack(Material.PHANTOM_MEMBRANE);
ItemMeta bpsMeta = backpacksmall.getItemMeta();
bpsMeta.setCustomModelData(1);
bpsMeta.setDisplayName("Small Backpack");
backpacksmall.setItemMeta(bpsMeta);
bpsRecipe = new ShapedRecipe(NamespacedKey.minecraft("backpack_small"), backpacksmall);
bpsRecipe.shape("LSL", "SCS", "LSL");
bpsRecipe.setIngredient('L', Material.LEATHER);
bpsRecipe.setIngredient('S', Material.STRING);
bpsRecipe.setIngredient('C', Material.CHEST);
plugin.getServer().addRecipe(bpsRecipe);

ItemStack backpackbig = new ItemStack(Material.PHANTOM_MEMBRANE);
ItemMeta bpbMeta = backpackbig.getItemMeta();
bpbMeta.setCustomModelData(2);
bpbMeta.setDisplayName("Large Backpack");
backpackbig.setItemMeta(bpbMeta);
bpbRecipe = new ShapedRecipe(NamespacedKey.minecraft("backpack_big"), backpackbig);
bpbRecipe.shape("LSL", "SBS", "LSL");
bpbRecipe.setIngredient('L', Material.LEATHER);
bpbRecipe.setIngredient('S', Material.STRING);
bpbRecipe.setIngredient('B', backpacksmall.getData());
plugin.getServer().addRecipe(bpbRecipe);
}

 

Shouldn't you cast plugin as
private Main plugin;

public RecipieManager() {
plugin = Main.getPlugin(Main.class);
}