input: Write a function to iterate over a list of numbers and print only the even numbers. The function should take a list of integers as input and return None. If the input list is empty, the function should return None without printing anything.
  assert print_even_numbers([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])==None
  assert print_even_numbers([2, 4, 6, 8, 10])==None
  assert print_even_numbers([1, 3, 5, 7, 9])==None
  assert print_even_numbers([])==None
output: def print_even_numbers(numbers):
      if not numbers:
          return None
      for num in numbers:
          if num % 2 == 0:
              print(num)
      return None