Datatable.AsEnumerable()

Datatable.AsEnumerable() giving me the error NullReferenceException: Object reference not set to an instance of an object

 using UnityEngine;
 using System.Data;
 using System.Linq;
 using System;
 
 public class CAS_Test : MonoBehaviour
 {
     // Start is called before the first frame update
     void Start()
     {
         DataTable testTable = new DataTable("testTable");
         Console.WriteLine(testTable.AsEnumerable());
     }
 }

Error

NullReferenceException: Object reference not set to an instance of an object System.Data.DataTableExtensions.AsEnumerable (System.Data.DataTable source) (at :0) CAS_Test.Start () (at Assets/CAS_Test.cs:12)

I have also tested with data in the data table. This happens only in Unity . I tested in with a c# compiler and the two lines works.

I need this to use Linq query.