public void AsString()
 {
     JValue value = null;
     Assert.IsNull(value.AsString());
     Assert.IsNull(JsonExtensions.Null().AsString());
     Assert.IsNull(new JObject().AsString());
     Assert.IsNull(new JValue(2.0).AsString());
     Assert.IsNull(new JValue(true).AsString());
     Assert.IsNull(new JArray().AsString());
     Assert.AreEqual("123", new JValue("123").AsString());
     value = new JValue("ABC");
     Assert.AreEqual("ABC", value.AsString());
 }