`findWhere`: Improved documentation and tests (2nd)

I lacked documentation for the return when it could not find a match.

The reason I have added two tests are for two reasons:
 * To assert that documentation is on the same page as the actual code.
 * As a regression test of future code changes.

This is the second iteration of #1146. The only difference between this pull request and the old one is that I've removed the overly pedantic examples.