docs: add missing javadocs

src/main/java/com/flowingcode/vaadin/addons/chatassistant/ChatAssistant.java

@@ -68,10 +68,18 @@ public class ChatAssistant extends Div {
   private boolean minimized = false;
   private Registration defaultSubmitListenerRegistration;
 
+  /**
+   * Default constructor. Creates a ChatAssistant with no messages.
+   */
   public ChatAssistant() {
     this(new ArrayList<>());
   }
 
+  /**
+   * Creates a ChatAssistant with the given list of messages.
+   * 
+   * @param messages the list of messages
+   */
   public ChatAssistant(List<Message> messages) {
     this.messages = messages;
     content.getElement().setAttribute("slot", "content");
@@ -148,9 +156,10 @@ public void clearWhoIsTyping() {
   }
 
   /**
-   * Sets the SubmitListener that will be notified when the user submits a message on the underlying messageInput
-   * @param listener
-   * @return
+   * Sets the SubmitListener that will be notified when the user submits a message on the underlying messageInput.
+   * 
+   * @param listener the listener that will be notified when the SubmitEvent is fired
+   * @return registration for removal of the listener
    */
   public Registration setSubmitListener(ComponentEventListener<SubmitEvent> listener) {
     defaultSubmitListenerRegistration.remove();