Exception in thread AWT-EventQueue-0 javalangNullPointerException Cannot invoke javaioPrintWriterprintlnString because thiswriter is null at GUIClientWindowactionPerformedClientWindowjava63 at javades

The exception is a NullPointerException and is caused by trying to invoke the println() method on a PrintWriter object that is null. The error occurs on line 63 of the ClientWindow class in the actionPerformed() method. The this.writer object has not been initialized or assigned a value, so it is null. To fix the error, the this.writer object should be initialized before trying to use it.