fix: mn create fails since 4.3.0 (#2319)

In 4.3.0 when we added chatbot creation, we abstracted the builder commands away.

At one point, we combine application-type features and user specified features into a single set.

The issue here is that the set in the case of the create command was unmodifiable.

This then failed with the esoteric 'Error null' message.

This PR takes the features from the application type, and loads them into a HashSet prior to doing any manipulation.

I did it this way as it's hard to test this area of the functionality, and it will prevent us having a similar issue if we add further commands

Closes #2318

starter-cli/src/main/java/io/micronaut/starter/cli/command/BuilderCommand.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2023 original authors
+ * Copyright 2017-2024 original authors
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -44,12 +44,12 @@
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.Callable;
 import java.util.function.Function;
 import java.util.function.Supplier;
-import java.util.stream.Collectors;
 
 import static picocli.CommandLine.Help.Ansi.AUTO;
 
@@ -83,7 +83,8 @@ public Integer call() throws Exception {
                     .parser(new DefaultParser())
                     .build();
             GenerateOptions options = createGenerateOptions(reader);
-            Set<String> selectedFeatures = options.getFeatures();
+            // options.getFeatures() may be an unmodifiable set, so unpack it into a modifiable set
+            Set<String> selectedFeatures = new HashSet<>(options.getFeatures());
             selectedFeatures.addAll(getFeatures(options.getApplicationType(), terminal, features));
             Project project = getProject(reader);
             try (OutputHandler outputHandler = new FileSystemOutputHandler(project, false, this)) {
@@ -106,7 +107,7 @@ public Integer call() throws Exception {
 
     protected List<String> getFeatures(ApplicationType applicationType, Terminal terminal, List<Feature> features) {
         AvailableFeatures availableFeatures = new BaseAvailableFeatures(features, applicationType);
-        List<String> featureNames = availableFeatures.getFeatures().map(Feature::getName).collect(Collectors.toList());
+        List<String> featureNames = availableFeatures.getFeatures().map(Feature::getName).toList();
         LineReader featuresReader = LineReaderBuilder.builder()
                 .terminal(terminal)
                 .completer(new StringsCompleter(featureNames))
@@ -123,7 +124,7 @@ protected List<String> getFeatures(ApplicationType applicationType, Terminal ter
             List<String> selectedFeatures = Arrays.asList(featuresLine.split(" "));
             List<String> invalidFeatures = new ArrayList<>();
             for (String name: selectedFeatures) {
-                if (!availableFeatures.findFeature(name).isPresent()) {
+                if (availableFeatures.findFeature(name).isEmpty()) {
                     invalidFeatures.add(name);
                 }
             }