Problème au lancement d'un "snake"

Bonjour, je suis cette année en Term.S et je fais la spécialité ISN. Je dois coder un Snake pour mon projet de fin d'année, mes connaissances en codage se limitant à de l'algorythmique, j'ai décidé de suivre ce tutoriel : https://michel-douez.developpez.com/articles/java/snake/#LVI , tout en apprenant le langage java en parallèle sur OpenClassRoom. Arrivé à l'étape IV, on me propose de tester le programme en regardant simplement l'incrémentation d'un entier. J'obtient cependant des messages d'exceptions bien qu'ayant respecté le tutoriel, voici le message d'erreur complet :

Exception in thread "Thread-1" java.lang.NullPointerException
 at JFenetre$2.run(JFenetre.java:38)
 at java.lang.Thread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
 at JFenetre$1.paintComponent(JFenetre.java:25)
 at javax.swing.JComponent.paint(Unknown Source)
 at javax.swing.JComponent.paintChildren(Unknown Source)
 at javax.swing.JComponent.paint(Unknown Source)
 at javax.swing.JLayeredPane.paint(Unknown Source)
 at javax.swing.JComponent.paintChildren(Unknown Source)
 at javax.swing.JComponent.paintToOffscreen(Unknown Source)
 at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
 at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
 at javax.swing.RepaintManager.paint(Unknown Source)
 at javax.swing.JComponent.paint(Unknown Source)
 at java.awt.GraphicsCallback$PaintCallback.run(Unknown Source)
 at sun.awt.SunGraphicsCallback.runOneComponent(Unknown Source)
 at sun.awt.SunGraphicsCallback.runComponents(Unknown Source)
 at java.awt.Container.paint(Unknown Source)
 at java.awt.Window.paint(Unknown Source)
 at javax.swing.RepaintManager$4.run(Unknown Source)
 at javax.swing.RepaintManager$4.run(Unknown Source)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
 at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
 at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
 at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
 at javax.swing.RepaintManager.access$1300(Unknown Source)
 at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
 at java.awt.event.InvocationEvent.dispatch(Unknown Source)
 at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
 at java.awt.EventQueue.access$500(Unknown Source)
 at java.awt.EventQueue$3.run(Unknown Source)
 at java.awt.EventQueue$3.run(Unknown Source)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
 at java.awt.EventQueue.dispatchEvent(Unknown Source)
 at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
 at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
 at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
 at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
 at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
 at java.awt.EventDispatchThread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
 at JFenetre$1.paintComponent(JFenetre.java:25)
 at javax.swing.JComponent.paint(Unknown Source)
 at javax.swing.JComponent.paintChildren(Unknown Source)
 at javax.swing.JComponent.paint(Unknown Source)
 at javax.swing.JLayeredPane.paint(Unknown Source)
 at javax.swing.JComponent.paintChildren(Unknown Source)
 at javax.swing.JComponent.paintToOffscreen(Unknown Source)
 at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
 at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
 at javax.swing.RepaintManager.paint(Unknown Source)
 at javax.swing.JComponent.paint(Unknown Source)
 at java.awt.GraphicsCallback$PaintCallback.run(Unknown Source)
 at sun.awt.SunGraphicsCallback.runOneComponent(Unknown Source)
 at sun.awt.SunGraphicsCallback.runComponents(Unknown Source)
 at java.awt.Container.paint(Unknown Source)
 at java.awt.Window.paint(Unknown Source)
 at javax.swing.RepaintManager$4.run(Unknown Source)
 at javax.swing.RepaintManager$4.run(Unknown Source)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
 at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
 at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
 at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
 at javax.swing.RepaintManager.access$1300(Unknown Source)
 at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
 at java.awt.event.InvocationEvent.dispatch(Unknown Source)
 at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
 at java.awt.EventQueue.access$500(Unknown Source)
 at java.awt.EventQueue$3.run(Unknown Source)
 at java.awt.EventQueue$3.run(Unknown Source)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
 at java.awt.EventQueue.dispatchEvent(Unknown Source)
 at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
 at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
 at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
 at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
 at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
 at java.awt.EventDispatchThread.run(Unknown Source)

J'en appelle à vous car je suis dépassé à ce niveau... Merci d'avance de votre aide !