Undefined index: und at weight_form_node_admin_content_alter()

I keep getting these messages when access admin/content:

Notice: Undefined index: und at weight_form_node_admin_content_alter() (line 124 from sites/all/modules/weight/weight.module).

Current workaround is to substitute line 124 from weight.module with the following code:

#default_value' => isset($node->weight[LANGUAGE_NONE][0]['value']) ? $node->weight[LANGUAGE_NONE][0]['value'] : 0,

But I have no idea whether this is the origin of the problem or just a symptom.