Call to a member function getConfigDependencyName() on null when adding a block

Reproduction:

1. Create a search api page
2. Add a block to any region

=>

Call to a member function getConfigDependencyName() on null in Drupal\search_api_page\Plugin\Block\SearchApiPageBlock->calculateDependencies() (line 56 of modules/contrib/search_api_page/src/Plugin/Block/SearchApiPageBlock.php).

Code

/**
   * {@inheritdoc}
   */
  public function calculateDependencies() {
    /* @var $search_api_page \Drupal\search_api_page\SearchApiPageInterface */
    $search_api_page = SearchApiPage::load($this->configuration['search_api_page']);
    $config_name = $search_api_page->getConfigDependencyName();
    return ['config' => [$config_name]];
  }

Problem

$this->configuration doesn't contain a "search_api_page" value at this point.

Proposed solution

Unclear. Check if calculateDependencies() is right here and if the timing / execution order is designed for that.