Exception thrown on invalid value for Enum in model
An exception is thrown when an incorrect value is received for an enum parameter in a model. Don't know how to handle the exception

This code throws an exception when the POST is sent with an incorrect value in 'k'
```
import happyx

type
  Kind = enum
    circle
    square

model Obj:
  k: Kind
  st: string

serve("127.0.0.1", 5000):
  post "/[data:Obj:json]":
    echo data
    return ""
```

This is run with:
* happyx-3.9.0
* Nim devel
* OS: Archlinux
