How to take ownership of elements in a script

[S1arhei]

@Ewan_Opie

import clr

clr.AddReference("RevitServices")
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager

clr.AddReference("RevitAPI")
import Autodesk
from Autodesk.Revit.DB import *

clr.AddReference('System.Core')
from System.Collections.Generic import *

doc = DocumentManager.Instance.CurrentDBDocument
uiapp = DocumentManager.Instance.CurrentUIApplication
app = uiapp.Application

def ToList(x):
    if isinstance(x,list):
        return UnwrapElement(x)
    else:
        return [UnwrapElement(x)]

def GetWorkset(item):
	if hasattr(item, "WorksetId"): return item.Document.GetWorksetTable().GetWorkset(item.WorksetId)
	else: return None

elem = ToList(IN[0])

wks = [GetWorkset(e) for e in elem]

iDs = [w.Id for w in wks]
Ids = List[WorksetId](iDs)

TransactionManager.Instance.ForceCloseTransaction()

try: checkedout_wks = WorksharingUtils.CheckoutWorksets(doc,Ids)
except Exception,er: checkedout_wks = str(er)

OUT = checkedout_wks

Same error: "AttributeError: ‘NoneType’ object has no attribute ‘Id’ ".
Does anybody mind to share the solution?