A patch for Rails 5 (with Oracle) and Enumerize

string.rb

#
# activemodel-5.0.0.1/lib/active_model/type/string.rb
#
module ActiveModel
  module Type
    class String < ImmutableString # :nodoc:

      ...

      def serialize(value)
        case value
        when ::String then value.to_s
        else super
        end
      end

      ...

    end
  end
end