Greetings.  I'm trying to create an extension method on System.Guid.  The code compiles, but when i try to use it, the method is not availble.  Here's the code and it compiles:

namespace Common.Utilities.GuidUtilities
{
    public static class GuidExtensions
    {
        public static bool IsNullOrEmptyGuid(this Guid? guid)
        {
            bool isNullorEmptyGuid = false;

            if (guid == null || guid == Guid.Empty)
                isNullorEmptyGuid = true;

            return isNullorEmptyGuid;
        }
    }
}

So when i try to use the code:  I include the namespace, but when I type System.Guid, method IsNullorEmptyGuid is not available.
Any help is appreciated.  Thank you.