NoneType object has no attribute AsString

Revit
,
3

I made schedule of specialty equipment in Revit, deleted the items having no values and some whose Item Number was greyed out and run the script. Still the error persists.

Can we somehow bypass those items by making changes in below code ?

import sys

import clr

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

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

clr.AddReference('ProtoGeometry')
from Autodesk.DesignScript.Geometry import *

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

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

elements = IN[0]
Item_Number = IN[1]
#parameter = IN[1]

outList = []


for i in UnwrapElement(elements):
	if i.LookupParameter("Item Number").AsString() == IN[1]:
		outList.append(i)


OUT = outList
AttributeError: 'NoneType' object has no attribute 'AsValueString