Warning: date_format() expects parameter 1 to be DateTime, boolean given in Drupal\node\NodeFormController->form() (line 202 of

Warning generated when editing a node and don't permitted save, generate error message "You have to specify a valid date."

On Drupal\node\NodeFormController

before
$node->date = format_date($node->getCreatedTime(), 'custom', 'Y-m-d H:i:s O');
after
$node->date = format_date($node->getCreatedTime(), 'custom', 'Y-m-d HH:mm:ss Z');

Example:
print_r($node->getCreatedTime());//1377543481
$node->date = format_date($node->getCreatedTime(), 'custom', 'Y-m-d H:i:s O');
print_r($node->date); //2013-58-26 15::
$node->date = format_date($node->getCreatedTime(), 'custom', 'Y-m-d HH:mm:ss Z');
print_r($node->date); //2013-58-26 15:58:01 -0300

Warning: date_format() expects parameter 1 to be DateTime, boolean given in Drupal\node\NodeFormController->form() (line 202 of core/modules/node/lib/Drupal/node/NodeFormController.php).