input: Write a function to generate a random 6-digit number in Python. The function should use the `random` module to generate the number and print it. If the input is `None`, the function should still generate and print a random 6-digit number.
  
  def generate_6_digit_number():
      import random
      number = random.randint(100000, 999999)
      print(number)
  
  assert generate_6_digit_number() is None
  assert generate_6_digit_number() is None
output: def generate_6_digit_number():
      import random
      number = random.randint(100000, 999999)
      print(number)