Fixed Deprecated function: strpos(): Passing null.

core/modules/layout_builder/layout_builder.module

@@ -158,7 +158,7 @@ function layout_builder_entity_view_alter(array &$build, EntityInterface $entity
   // If the entity is displayed within a Layout Builder block and the current
   // route is in the Layout Builder UI, then remove all contextual link
   // placeholders.
-  if ($display instanceof LayoutBuilderEntityViewDisplay && strpos($route_name, 'layout_builder.') === 0) {
+  if ($display instanceof LayoutBuilderEntityViewDisplay && strpos(strval($route_name), 'layout_builder.') === FALSE) {
     unset($build['#contextual_links']);
   }
 }

core/modules/layout_builder/src/Cache/LayoutBuilderUiCacheContext.php

@@ -25,7 +25,7 @@ public static function getLabel() {
    * {@inheritdoc}
    */
   public function getContext() {
-    return 'is_layout_builder_ui.' . (int) (strpos($this->routeMatch->getRouteName(), 'layout_builder.') !== 0);
+    return 'is_layout_builder_ui.' . (int) (strpos(strval($this->routeMatch->getRouteName()), 'layout_builder.') !== FALSE);
   }
 
 }