Sheetnode field in group "Notice: Undefined index: und w sheetnode_node_validate()"

"Notice: Undefined index: und w sheetnode_node_validate()"

Content type has sheetnode field, and custom group:

custom_group
- sheetnode_field

On validation the error show up because one of $form_state['field'] = '#parents'

Solution:

In sheetnode.module 679 line add substr( $field_name, 0, 5 ) === "field" to if statment

function sheetnode_node_validate($node, $form, &$form_state) {
  $errors = form_get_errors();
  if (!empty($errors) && !empty($form_state['field'])) foreach ($form_state['field'] as $field_name => $field) {
    if (substr( $field_name, 0, 5 ) === "field" && $field[LANGUAGE_NONE]['field']['type'] == 'sheetfield' && !empty($form_state['input'][$field_name])) {