input: Write a python function to convert a linked list to a Python list.
  assert linkedlist_to_list(LinkedList(1)) == [1]
  assert linkedlist_to_list(LinkedList()) == []
  assert linkedlist_to_list(LinkedList(1).append(2).append(3)) == [1, 2, 3]
output: class LinkedList:
      def __init__(self, value=None):
          self.value = value
          self.next = None
  
      def append(self, value):
          if self.value is None:
              self.value = value
              return self
          else:
              current = self
              while current.next:
                  current = current.next
              current.next = LinkedList(value)
              return self
  
  def linkedlist_to_list(linked_list):
      result = []
      current = linked_list
      while current and current.value is not None:
          result.append(current.value)
          current = current.next
      return result