On MRI 2.0.0 strings are not converted into integers for foreign keys

[ghost]

I became in use to pass HTTP params into DataMapper and it is typecasting data as needed.
Works perfect with Ruby prior to 2.0.0.

On 1.9* {'country_id' => '1'} works as expected.
On 2.0.0 it complains country_id should not be empty,
while {'country_id' => 1} works.
No custom validations used.

Any clue on how to fix this?
Typecasting data by hand is not an option.