cypriss/mutations — pull request #9 by dplummer (2013-03-02 00:46:01+00:00)
Title: Add the :default option for the StringFilter

Can't add @default_options[:default] = nil because then has_default?
will return true and the HashFilter will break.

Example:

```ruby
class StringExample < Mutations::Command
required do
string :name, default: "John Doe"
end
end

StringExample.new.inputs
# => {"name"=>"John Doe"}
```