input: Write a function to create a Python generator that returns numbers from a given list. If the given list is empty, the generator should yield `None`. 
  
  def list_generator(input_list):
      if not input_list:
          yield None
      else:
          for item in input_list:
              yield item
  
  assert list(list_generator([1, 3, 5, 7, 9])) == [1, 3, 5, 7, 9]
  assert list(list_generator([])) == [None]
output: def list_generator(input_list):
      if not input_list:
          yield None
      else:
          for item in input_list:
              yield item