input: Write a function to generate a random string of length 8 made of uppercase letters and numbers. If the input is provided, it should be used as the seed for the random generation.
  assert random_string_generator('seed_string')=='AB12EF3G'
  assert random_string_generator('another_seed')=='X9YZ45AB'
  assert random_string_generator('')=='8FGH7JKL'
  assert random_string_generator('test_seed')=='MN34OP56'
  assert random_string_generator(None)=='QR78ST9U'
output: import random
  import string
  
  def random_string_generator(seed=None):
      if seed is not None:
          random.seed(seed)
      return ''.join(random.choices(string.ascii_uppercase + string.digits, k=8))