Error message

• Notice: Undefined index: und in nnu_citation_metatags_node_view() (line 16 of /var/www/scholar/sites/all/modules/nnu_citation_metatags/nnu_citation_metatags.module).
• Warning: Invalid argument supplied for foreach() in nnu_citation_metatags_node_view() (line 16 of /var/www/scholar/sites/all/modules/nnu_citation_metatags/nnu_citation_metatags.module).