Issue #3269783 by RenatoG: Implement an early return on service to preprocess...

      return;

    }

    // If there is no block with this ID, skip.

    if (empty(Block::load($variables['elements']['#id']))) {

      return;

    }

    // Load the block by ID.

    $block = Block::load($variables['elements']['#id']);

    // Verify if the current block has Third Party Settings with classes.

    if ($block && $classes = $block->getThirdPartySetting('block_class', 'classes')) {

    $classes = $block->getThirdPartySetting('block_class', 'classes');

    if (!empty($classes)) {

      // Get all classes if exists.

      $classes_array = explode(' ', $classes);