config/install/jsonld.settings.yml

 remove_jsonld_format: false
+rdf_namespaces: []

jsonld.post_update.php

+<?php
+
+/**
+ * @file
+ * Post-update hook implementations.
+ */
+
+/**
+ * Ensure `rdf_namespaces` exists.
+ */
+function jsonld_post_update_ensure_rdf_namespaces_exists() : void {
+  $config = \Drupal::configFactory()->getEditable('jsonld.settings');
+
+  if ($config->get('rdf_namespaces') === NULL) {
+    $config->set('rdf_namespaces', [])->save();
+  }
+}

src/JsonldServiceProvider.php

 <?php
 
-namespace Drupal\Jsonld;
+namespace Drupal\jsonld;
 
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\DependencyInjection\ServiceModifierInterface;