input: Write a function that defines a class to create a linked list in Python using nodes. The class should have an `__init__` method that initializes the node with data and sets the next node to `None`.
  
  class ListNode:
      def __init__(self, data):
          self.data = data
          self.next = None
  
  assert ListNode(5).data == 5
  assert ListNode(5).next == None
output: def __init__(self, data):
      self.data = data
      self.next = None