Arrowhead

Code fixes based on comments and rubocop.
I think your `rescue/raise` stuff is probably in the wrong place. This will never raise, just return `nil`.
```
[1] pry(main)> {}.fetch :foo
KeyError: key not found: :foo
from (pry):1:in `fetch'
[2] pry(main)> h = {}; h[:foo]
=> nil
```