Empty many elements are not posting a blank string

[timriley]

Given a form with a many element like this:

many :collections do
  # fields here
end

When the many is empty, the form should post data like this: collections="" to indicate the emptiness of the structure. IIRC, this behaviour would be consistent with what we do for other array-like elements in Formalist?

Right now, this doesn't seem to be happening. Instead, the attribute is not submitted at all.

See #105 for a related issue. In the discussion there, you seem to indicate, @makenosound, that we're already posting an empty string. Perhaps the behaviour changed since then?