nil_object.rb

# in controller action:
def show
  @movie = Movie.find_by_id(params[:id]) # what if this movie not in DB?
  # BUG: we should check @movie for validity here!
end

-# ...later, in the Haml view:

%h1= @movie.title
-# will give "undefined method 'title' for nil:NilClass" if @movie is nil