Issue #3432296: issue of undefined array key

epub_reader_framework.install

@@ -9,6 +9,7 @@
  * Implements hook_requirements().
  */
 function epub_reader_framework_requirements($phase) {
+  $requirements = []; 
   if ($phase == 'runtime') {
     /** @var \Drupal\Core\StreamWrapper\StreamWrapperManager $stream_wrapper_manager */
     $stream_wrapper_manager = \Drupal::service('stream_wrapper_manager');