input: Write a function to create a linked list in Python using a class with nodes. The function should take a list of integers as input and return the head of the linked list. If the input list is empty, the function should return None.
  assert create_linked_list([1, 2, 3])==ListNode(1)
  assert create_linked_list([4, 5, 6])==ListNode(4)
  assert create_linked_list([])==None
output: def create_linked_list(lst):
      if not lst:
          return None
      head = ListNode(lst[0])
      current = head
      for value in lst[1:]:
          current.next = ListNode(value)
          current = current.next
      return head