AttributeError: 'List[object]' object has no attribute 'id' trying to filter elements

Revit
13

whats your imput? values or elements?

Object has no Id. Sounds like the imput is not correct!

import System
import clr

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

clr.AddReference('RevitAPIUI')
from Autodesk.Revit.UI import *

clr.AddReference('System')
from System.Collections.Generic import List

clr.AddReference('RevitNodes')
import Revit
clr.ImportExtensions(Revit.GeometryConversion)
clr.ImportExtensions(Revit.Elements)

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

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)]

elem = ToList(IN[0])

Ids = List[ElementId]()
for el in elem:
	Ids.Add(el.Id)

try: checkedout_el = WorksharingUtils.CheckoutElements(doc,Ids)
except Exception,er: checkedout_el = str(er)

OUT = checkedout_el