materio-d8/patches/hook_flag_access_id_on_null_4.patch

diff --git a/flag_lists.module b/flag_lists.module
index cd81104..8a83435 100644
--- a/flag_lists.module
+++ b/flag_lists.module
@@ -240,23 +240,29 @@ function flag_lists_flag_action_access($action, FlagInterface $flag, AccountInte
   $flagListsService = Drupal::service('flaglists');
   $flagLists = $flagListsService->getAllFlaggingCollections();
   foreach ($flagLists as $flagList) {
-    if ($flag->id() == $flagList->getRelatedFlag()->id()) {
-      if ($flagList->getBaseFlag()->isGlobal()) {
-        // The flag list is global.
-        return AccessResult::allowedIfHasPermission($account,
-          'access global flag lists');
-      }
-      elseif ($flagList->getOwnerId() == $account->id()) {
-        // The flag list is owned by current user.
-        return AccessResult::allowedIfHasPermission($account,
-          'view own flag lists');
-      }
-      else {
-        // The user is allowed to see all flag lists.
-        return AccessResult::allowedIfHasPermission($account,
-          'view flag lists');
+    if ($flagList->getRelatedFlag()) {
+      if ($flag->id() == $flagList->getRelatedFlag()->id()) {
+        if ($flagList->getBaseFlag()->isGlobal()) {
+          // The flag list is global.
+          return AccessResult::allowedIfHasPermission($account,
+            'access global flag lists');
+        }
+        elseif ($flagList->getOwnerId() == $account->id()) {
+          // The flag list is owned by current user.
+          return AccessResult::allowedIfHasPermission($account,
+            'view own flag lists');
+        }
+        else {
+          // The user is allowed to see all flag lists.
+          return AccessResult::allowedIfHasPermission($account,
+            'view flag lists');
+        }
       }
+    } else {
+      $logger = \Drupal::logger('flag_lists');
+      $logger->error('flagging_collection ' . $flagList->getName() . ' (' . $flagList->id() . ')' . ' owned by user id ' . $flagList->getOwner()->id() . ' doesn\'t have related flag');
     }
+    
   }
 
   // Check for access for the used template as well.