Error response when fields could not be found

Updated for all types.

I know there are `eval`s all over the code, but we're trying to move away from that.  Could we do this?

At the top of the file, in the use statements add `use Try::Tiny`; (the `use` statements should be alpha sorted).  Then you can do something like:

```
try { $c->stash( $file->{_source} || $file->{fields} ) }
catch { $c->detach( '/fields_not_found', [$_] ) };
```