anonimous

Im working in my own project. Im trying to show flag to anonimous users whith flag module, flag_anon module and session api. I can see de flags like text no links and without icons and the system show me this error message: Notice: Undefined index: content_id en flag_anon_preprocess_flag() (línea 213 de /homepages/xx/xsites/all/modules/flag_anon/flag_anon.module).
And the line 213 in flag_anon.module is:

$content_id = $variables['content_id'];

Somebody has any idea about what or where is the problem.