Issue #3487733: TypeError: array_filter(): Argument #1 ($array) must be of...

Issue #3487733: TypeError: array_filter(): Argument #1 ($array) must be of type array, null given in array_filter() (line 349 of /Drupal/Core/Datetime/Element/Datelist.php)

Closes #3487733

core/lib/Drupal/Core/Datetime/Element/Datelist.php

@@ -346,7 +346,7 @@ protected static function checkEmptyInputs($input, $parts) {
     // \Drupal\Core\Datetime\Element\Datelist::valueCallback().
     unset($input['object']);
     // Filters out empty array values, any valid value would have a string length.
-    $filtered_input = array_filter($input, 'strlen');
+    $filtered_input = array_filter($input ?? [], 'strlen');
     return array_diff($parts, array_keys($filtered_input));
   }