Configure --missing-key-action on a per-variable basis.

[josh-padnick]

Boilerplate currently supports the --missing-key-action property when using boilerplate on the command line.

The problem is that I want certain values to render blank, while other values that are accidentally blank (or otherwise invalid) to throw an error. But boilerplate makes me choose just one --missing-key-action approach for the entire template generation.

[brikis98]

Distinguishing between an empty string and a missing value is a known TODO. A potential workaround for now is to use some sort of placeholder value (e.g. __EMPTY__) to indicate you want an empty string.