We have this code:

```
// using ServiceStack JSONSerializer
string typeInfoString = JsonSerializer.SerializeToString<Type>(typeof(HashSet<string>));
// yields "System.Collections.Generic.HashSet`1[[System.String, mscorlib]], System.Core"

// this string is the same thing, so it's probably valid json
string jsonTypeInfo = typeof(HashSet<string>).ToJson();

// this should work, I feel like
Type desType = JsonSerializer.DeserializeFromString<Type>(jsonTypeInfo);
// but desType ends up being null :(

```

Is there some ServiceStack gotcha about the HashSet type?