input: Write a python function to create a linked list from a list of values.
  assert linked_list_from_values([1, 2, 3, 4]).data == 1
  assert linked_list_from_values([1, 2, 3, 4]).next.data == 2
  assert linked_list_from_values([1, 2, 3, 4]).next.next.data == 3
  assert linked_list_from_values([1, 2, 3, 4]).next.next.next.data == 4
output: class ListNode:
      def __init__(self, data=0, next=None):
          self.data = data
          self.next = next
  
  def linked_list_from_values(values):
      if not values:
          return None
      head = ListNode(values[0])
      current = head
      for value in values[1:]:
          current.next = ListNode(value)
          current = current.next
      return head