public void RequiredNotNullThrowsExceptionWhenNull()
        {
            NullableExtensionTests nullObject = null;

            Assert.Throws <InvalidStateException>(() => nullObject.RequiredNotNull());
        }
        public void RequiredNotNullReturnsThisWhenNotNull()
        {
            var nonNullObject = new NullableExtensionTests();

            Assert.Equal(nonNullObject, nonNullObject.RequiredNotNull());
        }