This small patch registers a new `ActiveModel` type: `array`.
It will split a string on `,` to create a new array. If the value is
already an array, nothing will happen and for all other types, it will
wrap the value in an array.
Here’s an example on an existing contract:
```ruby
attribute :target_usernames
before_validation do
self.target_usernames =
(
if target_usernames.is_a?(String)
target_usernames.split(",")
else
target_usernames
end
)
end
# can be rewritten as:
attribute :target_usernames, :array
```
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