input: Write a Python function that accepts an array of integers and computes the sum of their absolute values, after being multiplied by the product of their signs. If the array is empty, it should return None.
  assert calculate_value([1, 2, 2, -4]) == -9
  assert calculate_value([0, 1]) == 0
  assert calculate_value([1, 1, 1, 2, 3, -1, 1]) == -10
  assert calculate_value([]) == None
  assert calculate_value([2, 4,1, 2, -1, -1, 9]) == 20
  assert calculate_value([-1, 1, -1, 1]) == 4
  assert calculate_value([-1, 1, 1, 1]) == -4
  assert calculate_value([-1, 1, 1, 0]) == 0
output: def calculate_value(arr):
      if not arr:
          return None
      sign_product = 1
      for num in arr:
          if num != 0:
              sign_product *= (num // abs(num))
          if sign_product == 0:
              return 0
      return sign_product * sum(abs(num) for num in arr)