C# Check for !null and string.Empty on a JSON response throws FormatException

Question

I wrote a simple API call within a method expecting a JSON response... Nothing spectacular:

// [API call...]

dynamic responseString = JsonConvert.DeserializeObject(response.Result.Content.ReadAsStringAsync().Result);
item.category               = responseString.category;
item.shortDescription       = responseString.shortDescription;
item.countryOfManufacture   = responseString.manufacturerCountry ?? "DE";

Sometimes there are not all required parameters from the API available... So I tried to check for is null and is string.Empty and raise a dialog where the user can enter the missing values...

But this:

            if (responseString.weight == null ||responseString.weight == string.Empty )
            {
                DialogArgs args = new DialogArgs();
                args.Add("Gewicht");
                OnMissingValue?.Invoke(args);
                item.weight = args.Get<float>("Gewicht");
            }
            else
            {
                item.weight = Convert.ToSingle(responseString.weight) / 1000;
            }

or

if (string.IsNullOrEmpty(responseString.weight))

throws a FormatException. If I check either is null or is string.Empty it works like a charm. I know the differnence between ref and value types and thought maybe there is a Problem... However, I like to know why it behaves like this...

Thanks in advance... and sorry for my english...

Markus

Answer 1

Ok, I get it... The dynamic descriptor is the reason. You have to cast it to a string like this:

if (string.IsNullOrEmpty((string)responseString.weight))

...thanks for your effort

Markus