Passing empty string for option on command is set to undefined

[sorohan]

For this program:

program
  .name('test')
  .command('mycommand')
  .option('-c, --cheese [type]', 'optionally specify the type of cheese')
  .action(function(cmd) {
    val = cmd.cheese;
  });

And calling it like this:

test mycommand --cheese ""

I would expect the value of "val" to be an empty string, but it is actually undefined.