using System;

using System.Collections.Generic;

using System.Linq;

public class TestObj

{

    public string Field{get;set;}

}

​

public class Program

{

    public static void Main()

    {

        var list = new List<TestObj>()

        {

            new TestObj

            {

                Field = "true"

            },

            new TestObj

            {

                Field = "false"

            },

            new TestObj

            {

                Field = null

            }

        };

        //var res = list.Where(x=> !string.IsNullOrWhiteSpace(x.Field) && x.Field.Equals("true", StringComparison.InvariantCultureIgnoreCase)).ToList();

        //var res = list.Where(x=> x.Field.Equals("true", StringComparison.InvariantCultureIgnoreCase));

        //var res = list.Where(x=> x.Field.Equals("true", StringComparison.InvariantCultureIgnoreCase)).ToList();

        var res = list.Where(x=> x.Field=="true").ToList();

        Console.WriteLine(res.First().Field);

    }

}