JSON input binding error of type InvalidCastException

Just a suggestion, when I get a JSON input binding of this type :
```System.InvalidCastException at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType```
for an HttpTrigger, the runtime returns a 500 error.

I think most of the time, if not all the time, this can be treated as a 4xx error, probably a 422 since the input I received, failed validation.