inhectors

==begin
  def self.options_for_select(story)
    options = []
    options << ["",""] if story.story_type_id.nil?
    all.map{|story_type| options<<[story_type.title,story_type.id]}
    options
  end
==end

irb(main):021:0> [1,2,5].inject( true ? [nil] : [] ){|a, b| a + [b, 1]}
=> [nil, 1, 1, 2, 1, 5, 1]
irb(main):022:0> [1,2,5].inject( false ? [nil] : [] ){|a, b| a + [b, 1]}
=> [1, 1, 2, 1, 5, 1]

Conclusion

def self.options_for_select(story)
  self.all.inject(story.story_type.present? ? [] : [nil]) {|options, item| options + [item.title, item.id]}
end