Foreman Create Host by API and DHCP failed

Hi to everyone.
I met a big problem. When I try to create an host with a specific POST,
Foreman give me back a specific error: {Error : [mac is blank!]}.
The mac should be self-generated by Foreman self. So, how Can I fix this
problem?? I try to change my POST in some way but result not changed.

This is the specific error in production.log:

Started POST "/hosts" for at Tue Jun 25 12:31:10 +0200 2013
Processing by HostsController#create as JSON
Parameters:* {"capabilities"=>"build", "host"=>{"disk"=>"",
"managed"=>"true", "puppetclass_ids"=>["", "51", "52", "53"], "build"=>"1",
"puppet_proxy_id"=>"1", "compute_resource_id"=>"1", "model_id"=>"",
"is_owned_by"=>"", "name"=>"hostivanoapi", "operatingsystem_id"=>"4",
"size_gb"=>"8", "storage_domain"=>"a646d974-19be-4a8d-bf68-a3974d46a823",
"id"=>""}, "new_volumes"=>{"_delete"=>"", "size_gb"=>"",
"storage_domain"=>"a646d974-19be-4a8d-bf68-a3974d46a823", "id"=>""}},
"cores"=>"1", "memory"=>"536870912",
"_delete"=>"", "name"=>"nic1"},
"_delete"=>"", "name"=>""}},
"cluster"=>"3e49d61c-9eb7-4c90-9ac8-9c757719c187", "start"=>"0"},
"progress_report_id"=>"[FILTERED]", "subnet_id"=>"1",
"name"=>"", "provider"=>"IPMI", "mac"=>"", "ip"=>"", "domain_id"=>"1",
"type"=>"Nic::Managed"}}, "mac"=>"", "environment_id"=>"1",
"medium_id"=>"1", "overwrite"=>"false", "comment"=>"", "enabled"=>"1",
"ptable_id"=>"1", "ip"=>"", "domain_id"=>"1",
Authorized user admin(Admin User)
Adding Compute instance for
Removing Compute instance for
mac value is blank!
Rolling back due to a problem: Querying instance details for 3 failed
Removing Compute instance for
Failed to save: mac value is blank!
Completed 422 Unprocessable Entity in 1753ms (Views: 0.7ms | ActiveRecord:

Sorry I forgot an important detail. The Foreman version is 1.1RC4. Thanks
in advance for your help.