Sandi Metz suspicion of nil (pbox2d example)

Late last year Sandi Metz blogged about Suspicions of nil, more recently she presented Nothing is Something at Bath ruby, and I just watched the video at confreaks. The timing could not be much better I had just translated Dan Shiffmans MouseJoint sketch to run with ruby-processing, and the Spring class which has all these egregious checks for null (or nil in initial ruby version). I found that by using ruby duck-typing I could create a DummySpring class, that got rid of all those suspicious null checks!!!
The DummySpring class

# dummy_spring.rb by Martin Prout
# using duck-typing so class can stand in for Spring

# Using this class avoids test for nil
class DummySpring
  def initialize; end

  # If it exists we set its target to the mouse location
  def update(_x, _y); end

  def display; end

  # This is the key function where
  # we attach the spring to an x,y location
  # and the Box object's location
  def bind(x, y, box)
    spring = Spring.new
    spring.bind(x, y, box)
    spring
  end

  def destroy; end
end

The only slightly tricky thing was the sketch needs to know that DummyString bind returns an instance of Spring, but otherwise it all looks pretty cool. Would make a good example except that pbox2d confounds things (we have two worlds a jbox2d physics world and a processing sketch world, and we track both).