input: Write a function to remove all duplicate elements from a list and preserve the original order. If the input list is empty, return an empty list.
  
  def remove_duplicates(nums):
      new_list = []
      for num in nums:
          if num not in new_list:
              new_list.append(num)
      return new_list
  
  assert remove_duplicates([1, 3, 3, 5, 5, 7])==[1, 3, 5, 7]
  assert remove_duplicates([1, 1, 1, 1, 1])==[1]
  assert remove_duplicates([])==[]
  assert remove_duplicates([1, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
output: def remove_duplicates(nums):
      new_list = []
      for num in nums:
          if num not in new_list:
              new_list.append(num)
      return new_list