Demonstrating LINQ query with 1) check for null list, 2) check for null list items, and 3) check for null property before querying on it.

LinqNullChecks.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApplication
{
	class Program
	{
		static void Main()
		{
			var people = new List<Person>
			{
				new Person { Name = "Justin", Occupation = "Software Engineer" },
				null,
				new Person { Name = "Anthony", Occupation = "Software Developer" },
				new Person { Name = "Daniel", Occupation = null },
				new Person { Name = "Matthew", Occupation = "Lead Engineer" }
			};

			List<Engineer> engineers = (people == null) ? null :
				people.Where(p => (p != null)
						&& !string.IsNullOrWhiteSpace(p.Occupation)
						&& p.Occupation.Contains("Engineer"))
					.Select(p => new Engineer { Name = p.Name })
					.ToList();

			foreach (Engineer engineer in engineers)
				Console.WriteLine(engineer.Name);

			Console.ReadKey();
		}

		private class Person
		{
			internal string Name { get; set; }
			internal string Occupation { get; set; }
		}

		private class Engineer
		{
			internal string Name { get; set; }
		}
	}
}