If no pdf default format is provided, a notice is popuped when you go to the generate pdf page

to reproduce :
add at least one pdf format (without making any of it the default one) and add an associated model
List some contact (one is enough), select it, action -> print pdf and a notice will appear :

"""
Notice : Undefined index: id dans CRM_Contact_Form_Task_PDFLetterCommon::setDefaultValues() (ligne 153 dans /var/www/drupal/sites/all/modules/civicrm/CRM/Contact/Form/Task/PDFLetterCommon.php).
"""

In fact the default format recovered by this function :

"""
$defaultFormat = CRM_Core_BAO_PdfFormat::getDefaultValues();
"""

doesn't provide the 'id' information and the notice is due to :

"""
$defaultFormat['format_id'] = $defaultFormat['id'];
"""

the following test is sufficient to avoid notices and warnings (see attached patch):

"""
if (isset($defaultFormat['id'])){
$defaultFormat['format_id'] = $defaultFormat['id'];
}
"""

But ensuring that getDefaultValues returns normalized datas seems a better choice.
Hoping this helps