input: Write a function to create a linked list in Python using the given class template. The function should take a list of integers as input and return the head of the linked list.
  assert create_linked_list([1, 2, 3, 4]) == ListNode(1)
  assert create_linked_list([]) == None
output: def create_linked_list(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