input: Write a function to compress a given data sequence by grouping consecutive numbers with the same sign. If the sequence is empty, return an empty list. Use the following function signature:
  def compress_sequence(nums):
  
  Call Example 1:
  assert compress_sequence([9, -2, 6, 0, -7]) == [[9], [-2], [6, 0], [-7]]
  
  Call Example 2:
  assert compress_sequence([1, 1, -1, -1, 0, 0]) == [[1, 1], [-1, -1], [0, 0]]
  
  Call Example 3:
  assert compress_sequence([]) == []
output: def compress_sequence(nums):
      if not nums:
          return []
      result = []
      current_group = [nums[0]]
      for i in range(1, len(nums)):
          if (nums[i] >= 0 and nums[i-1] >= 0) or (nums[i] < 0 and nums[i-1] < 0):
              current_group.append(nums[i])
          else:
              result.append(current_group)
              current_group = [nums[i]]
      result.append(current_group)
      return result