I've done a little searching and found that all passed values are converted to a string before they are passed to the database.
This is done in rhom/rhom_object_factory.rb (rhodes version 22.214.171.124) on line 1617 (val = value.to_s).
The distinction between an empty string and nil is lost there.
Is there any progress on this bug?
Will it be fixed in a future release?