Fix bugs

src/GamePanel.java

@@ -30,6 +30,7 @@ public class GamePanel extends JPanel implements Runnable, KeyListener, Serializ
   public transient Thread gameThread;
   public transient Image image;
   public transient Graphics graphics;
+  public transient boolean isNewStart = false;
   public Player player;
   public BackgroundImage background, cloudOneBackground, cloudTwoBackground, cloudThreeBackground;
   public int playerFrame, enemyFrame;
@@ -113,6 +114,7 @@ public class GamePanel extends JPanel implements Runnable, KeyListener, Serializ
     // the height of 35 is set because it is half of the original tile height (i.e., 70px)
     addUserInterface();
     this.setPreferredSize(new Dimension(GAME_WIDTH, GAME_HEIGHT));
+    isNewStart = true;
   }
 
   public void addUserInterface() {
@@ -315,9 +317,11 @@ public class GamePanel extends JPanel implements Runnable, KeyListener, Serializ
 }
 
   //run() method is what makes the game continue running without end. It calls other methods to move objects,  check for collision, and update the screen
-  public void run(){
-    LevelManager.setLevel(1);
-    isDialogue = true;
+  public void run() {
+    if (isNewStart) {
+      LevelManager.setLevel(1);
+      isDialogue = true;
+    }
     //the CPU runs our game code too quickly - we need to slow it down! The following lines of code "force" the computer to get stuck in a loop for short intervals between calling other methods to update the screen. 
     long lastTime = System.nanoTime();
     double amountOfTicks = 60;

src/Player.java

@@ -225,7 +225,9 @@ public class Player extends GenericSprite {
       y-=1;
       isGrounded = false;
       if(canUpdate(0,-8)) {
-        jump.start();
+        if (jump != null) {
+          jump.start();
+        }
       }
       yVelocity = -10;
     }