Addressing warnings.

- SI-6923 uncovered a few valid warnings, these have been
   addressed.
 - A pair of "catches all throwable" warnings appeared; one
   of the is spurious and the subject of SI-6994.

Review by @JamesIry. What's your opinion on the spuriosity of the following?

```
scala> (x => x): (Any => Unit)
<console>:8: warning: a pure expression does nothing in statement position; you may be omitting necessary parentheses
              (x => x): (Any => Unit)
                    ^
```