Invalid filter values result in internal server error

[pehbehbeh]

Invalid filter values should not result in a 500 internal server error.

For example, the user filter on the post resource is a multi select filter. You can add more users by repeating the filters[user][] parameter in the URL:

/posts?filters[user_id][]=<user_id>&filters[user_id][]=<user_id>

But because we expect the multi select filter values to be in this structure, the following URL will return a 500 internal server error:

/posts?filters[user_id]=<user_id>

Either the filter values should be ignored in this case or a bad request should be returned by the server.

There is also an error if the given `user_id' is not a UUID.