Description

ValidationFailed is apparently a client error due to passing invalid params.
Thus, server should response 400 Bad Request instead of 500 Internal Server Error when ValidationFailed is raised.

Steps to Reproduce

1. Start a new amber project
2. Generate a scaffold with at least one field
3. POST it without params

Expected behavior: 400 Bad Request

Actual behavior: 500 Internal Server Error

Reproduces how often: always

Versions

v0.7.2 and master

Additional Information

I think @faustinoaq is ready to fix this.