viatropos/tower — pull request #350 by tremby (2012-11-14 10:07:21+00:00)
Title: set validation: validate as fine if we have null instead of iterable

Rationale: now I can skip/abort the validation conditionally such as with the
following:

```
in: ->
if @get('country') == 'CA'
['ON', 'QC', 'NS', 'NB', 'MB', 'BC', 'PE', 'SK', 'AB', 'NL', 'NT', 'YT', 'NU']
else
null
```

What do you think of this? This functionality would definitely be nice but maybe you have a different idea of how it should be implemented.