input: Write a python function that accepts a list of integers and returns the sum of their absolute values, multiplied by the product of their signs. Return None if the list is empty.
  assert prod_signs([1, 2, 2, -4]) == -9
  assert prod_signs([0, 1]) == 0
  assert prod_signs([1, 1, 1, 2, 3, -1, 1]) == -10
  assert prod_signs([]) == None
  assert prod_signs([2, 4,1, 2, -1, -1, 9]) == 20
  assert prod_signs([-1, 1, -1, 1]) == 4
  assert prod_signs([-1, 1, 1, 1]) == -4
  assert prod_signs([-1, 1, 1, 0]) == 0
output: def prod_signs(lst):
      if not lst:
          return None
      abs_sum = sum(abs(x) for x in lst)
      sign_product = 1
      for x in lst:
          sign_product *= 1 if x == 0 else (1 if x > 0 else -1)
      return abs_sum * sign_product