if args is falsy, assume a default collection.

This is kind of an edge case.
When the command's option is not required, and the option is not optional, and we follow the

```
 *      program
 *        .command(..)
 *        .description(..)
 *        .action(function(){
 *        });
```

pattern, then after some event chaining args happens to be `undefined` which breaks the flow.

Providing a default value if args do not exist, will make the function less error-prone nonetheless; and it won't cause any regression in the existing behavior.
Merge pull request #209 from v0lkan/feature/minor-action-fix

if args is falsy, assume a default collection.