Element::properties() replaces element_properties(), must be passed an array

This is a followup to element_* functions deprecated; use Element class methods instead.

The procedural Drupal 7 function element_properties() was replaced in Drupal 8 by \Drupal\Core\Render\Element::properties(). Previously, element_properties() technically would accept a non-array parameter, which would automatically be cast into an array. The analogous Element::properties() method only accepts arrays.

Before:

  $thing = new stdClass;
  $thing->{'#title'} = 'Foo';
  $thing_properties = element_properties($thing);

After:

  $thing = new stdClass;
  $thing->{'#title'} = 'Foo';
  $thing_properties = \Drupal\Core\Render\Element::properties( (array) $thing );