preseed partman-crypto: how to cancel erase data step

[Alexis de BRUYN <alexis.mailinglist@de-bruyn.fr>]

Hi Everybody,

I am trying to cancel the erase data step of the partman-crypto 
configuration via preseed (Jessie amd64).

The following lines are not working for me:
d-i partman-crypto/warn_erase boolean false
d-i partman-crypto/erase_data boolean false
d-i partman-crypto/confirm_erase_data boolean false

Is there something else I need to add?

Thanks for your help,

--
Alexis de BRUYN