Identify the error in this iterator implementation snippet:

Identify the error in this iterator implementation snippet:

class MyIterator:
  def __init__(self, collection):
    self.collection = collection
  def hasNext(self):
    return self.index < len(self.collection)
  def next(self):
    if self.hasNext():
      element = self.collection[self.index]
      self.index += 1
      return element
    else:
      raise StopIteration()

What is missing that causes a runtime error?