http://kijanawoodard.com/cool-feature-of-extension-methods/

cool.cs

using System;
 
namespace FizzBuzz
{
    public class ExtensionsDemo
    {
        public static void TestString()
        {
            var s = "hello";
            var ok = s.HasValue();
 
            s = null;
            ok = s.HasValue();
        }
    }
 
    public static class StringExtensionMethods
    {
        public static bool HasValue(this string value)
        {
            return !string.IsNullOrWhiteSpace(value);
        }
    }
}