review feedback: replace assert by Objects.requireNonNull

Author: Marcel Jacek

examples/serverupdate/src/main/java/cloud/stackit/sdk/serverupdate/examples/ServerUpdateExample.java

@@ -71,7 +71,7 @@ public static void main(String[] args) throws IOException {
 			System.out.println("List all available update policies:");
 			GetUpdatePoliciesResponse listUpdatePolicies =
 					serverUpdateApi.listUpdatePolicies(projectId);
-			assert listUpdatePolicies.getItems() != null;
+			Objects.requireNonNull(listUpdatePolicies.getItems());
 			for (UpdatePolicy policy : listUpdatePolicies.getItems()) {
 				System.out.println("*************************");
 				System.out.println("* Policy name: " + policy.getName());