Switched Java to 21, fixed JavaDoc warnings.

gson/src/main/java/de/neitzel/gson/adapter/InstantTypeAdapter.java

@@ -24,6 +24,17 @@ import java.time.format.DateTimeParseException;
  */
 public class InstantTypeAdapter implements JsonSerializer<Instant>, JsonDeserializer<Instant> {
 
+    /**
+     * Constructs a new {@code InstantTypeAdapter} instance.
+     * <p>
+     * This is a default, no-argument constructor for the {@link InstantTypeAdapter} class,
+     * which provides custom (de)serialization support for {@link Instant} objects in
+     * accordance with the ISO-8601 standard.
+     */
+    public InstantTypeAdapter() {
+        // Default constructor
+    }
+
     /**
      * Serializes an {@link Instant} object into its ISO-8601 string representation as a {@link JsonElement}.
      *

gson/src/main/java/de/neitzel/gson/config/JsonConfiguration.java

@@ -21,7 +21,6 @@ import java.util.Map;
  */
 @Builder(builderClassName = "ConfigurationBuilder")
 public class JsonConfiguration {
-
     /**
      * The name of the application.
      * This variable is used to identify the application and is incorporated into various configurations,
@@ -67,6 +66,21 @@ public class JsonConfiguration {
      */
     private final Gson gson;
 
+    /**
+     * Constructs a new {@code JsonConfiguration} instance with the specified parameters.
+     *
+     * @param appName  the name of the application
+     * @param homeDir  the home directory path for the application
+     * @param settings a map containing configuration settings as key-value pairs
+     * @param gson     the Gson instance used for JSON serialization and deserialization
+     */
+    public JsonConfiguration(String appName, String homeDir, Map<String, String> settings, Gson gson) {
+        this.appName = appName;
+        this.homeDir = homeDir;
+        this.settings = settings;
+        this.gson = gson;
+    }
+
     /**
      * Stores a key-value pair into the configuration settings.
      * The value is serialized into a JSON string before being stored.
@@ -206,6 +220,18 @@ public class JsonConfiguration {
          */
         private String homeDir = System.getProperty("user.home");
 
+        /**
+         * Default constructor for the {@code JsonConfigurationBuilder} class.
+         * Initializes a new instance of the {@code JsonConfigurationBuilder}.
+         * This constructor allows creation of a builder used for configuring
+         * {@code JsonConfiguration} instances, enabling the specification of
+         * application-specific settings such as the application name, home directory,
+         * and custom Gson adapters.
+         */
+        public JsonConfigurationBuilder() {
+            // Default constructor
+        }
+
         /**
          * Sets the application name to be used in the configuration.
          *