The database migration AddOwnerToHosts in db/migrate/20100419151910_add_owner_to_hosts.rb fails when being run with PostgreSQL as database.

$ rake db:migrate
(in /usr/share/foreman)
==  AddOwnerToHosts: migrating ================================================
-- add_column(:hosts, :owner_id, :integer)
   -> 0.0026s
-- add_column(:hosts, :owner_type, :string)
   -> 0.0007s
-- setting default owner for all hosts
rake aborted!
An error has occurred, this and all later migrations canceled:

PGError: ERROR:  invalid input syntax for integer: "" 
: UPDATE "hosts" SET owner_id = '' 

(See full trace by running task with --trace)

The value of owner.id, which is used in the migration, is not known at this stage of the migration.