public RecipeIngredient Create(Guid ingredientId, double grams)
{
if (grams <= 0)
{
throw new ArgumentException("Cant add ingredients with grams lower than zero.");
}
var id = new Identity <Guid>(ingredientId);
return(_ingredientRepository.ExistById(id.Value)
? new RecipeIngredient(id, grams)
: throw new ArgumentNullException($"Ingredient with Id:{ingredientId} does not exist."));
}