Refactor: use yoda notation to get error in case of mistyping

src/main/java/ChatClient.java

@@ -20,7 +20,7 @@ public class ChatClient extends JFrame implements KeyListener {
         super("Chat");
         address = JOptionPane.showInputDialog("bitte IP-Adresse");
         
-        if (address != null) {
+        if (null != address) {
             receiveMessages();
         }
     }