public void NullProtection()
        {
            Assert.Throws <ArgumentNullException>(() => new SpannerStruct.Field("name", null, "value"));
            var value = new SpannerStruct();

            Assert.Throws <ArgumentNullException>(() => value.Add("name", null, "value"));
            Assert.Throws <ArgumentNullException>(() => value.Add(null));
        }