Support Lightning Core 5.x (Drupal core 8.8.x).

composer.json

@@ -9,7 +9,7 @@
         "drupal/autosave_form": "^1.0",
         "drupal/conflict": "2.0-alpha1",
         "drupal/diff": "^1.0",
-        "drupal/lightning_core": "^3.11 || ^4.1 || 3.x-dev || 4.x-dev",
+        "drupal/lightning_core": "3.* || 4.* || 5.*",
         "drupal/moderation_dashboard": "^1.0",
         "drupal/moderation_sidebar": "^1.2",
         "oomphinc/composer-installers-extender": "^1.1"

modules/lightning_scheduler/src/Plugin/Field/FieldWidget/ModerationStateWidget.php

@@ -112,11 +112,16 @@ class ModerationStateWidget extends BaseModerationStateWidget {
 
     // The latest revision, if there is one, is the canonical source of truth
     // regarding scheduled transitions.
-    $latest_revision = $this->moderationInformation
-      ->getLatestRevision(
-        $entity->getEntityTypeId(),
-        $entity->id()
-      ) ?: $entity;
+    if ($entity->isNew()) {
+      $latest_revision = $entity;
+    }
+    else {
+      $latest_revision = $this->moderationInformation
+        ->getLatestRevision(
+          $entity->getEntityTypeId(),
+          $entity->id()
+        ) ?: $entity;
+    }
 
     $transition_set = new TransitionSet(
       $latest_revision->get('scheduled_transition_date'),