When Testing for the Existence of Config Data, Use != nil

[dzoladz]

Per @phette23

use != nil instead of != '' to test if config data exists

Here's a comment that discusses the boolean logic of these values

We'll need to globally find and replace these tests, carefully and perhaps selectively at first. There are likely associated updates that will need to be made to configuration and data files. See PR #7 for and example.

[kaitlinnewson]

Could the preferred way to handle empty variables in the config and templates also be added to the style guide? This would be helpful to ensure we remain consistent going forward.

[dzoladz]

@ranti Would you be able to find an appropriate place in the above referenced style guide to add this info?