crafterm/comma — pull request #61 by eitoball (2013-08-03 14:01:24+00:00)
Title: Extract nil value

In CSV class, `nil` value has special meaning. For example,
```ruby
require 'csv'
puts CSV.generate { |csv| csv << [nil, ''] }
```
code above would produce `,""`. `nil` would become empty, no quotes around.

So, it would be nice if comma doesn't call `#to_s` on `nil` values.