Program: 98967
Project: 98967
Buggy source:
public PlayField createLevel(String jsonString){
  PlayField field=new PlayField();
  Gson gson=new Gson();
  Scanner scanner;
  try {
    scanner=new Scanner(new File(jsonString));
    String wholeFile=scanner.useDelimiter("String_Node_Str").next();
    Type collectionType=new TypeToken<GameFile>(){
    }
.getType();
    myGameInfo=gson.fromJson(wholeFile,collectionType);
  }
 catch (  FileNotFoundException e) {
    e.printStackTrace();
  }
  if (myGameInfo == null) {
    return null;
  }
  File backgroundPathFile=null;
  BufferedImage myBackground=null;
  try {
    backgroundPathFile=new File(myGameInfo.getBackground());
    myBackground=ImageIO.read(backgroundPathFile);
  }
 catch (  IOException e1) {
    System.out.print("String_Node_Str");
  }
  background=new ImageBackground(myBackground);
  field=new PlayField(background);
  myGame.CHARACTER=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.PROJECTILE=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.POWER_UP=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.PLATFORM=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.SPAWNPOINT=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.COINS=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.BAD_GUYS=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.SPRINGS=field.addGroup(new SpriteGroup("String_Node_Str"));
  ArrayList<LESprite> SpriteList=new ArrayList<LESprite>();
  SpriteList.add(new Bad_Guys());
  SpriteList.add(new Character());
  SpriteList.add(new Platform());
  for (int k=0; k < myGameInfo.getList().size(); k++) {
    ArrayList<String> LESpriteinfo=myGameInfo.getList().get(k);
    for (int i=0; i < SpriteList.size(); i++) {
      if (SpriteList.get(i).isInstanceOf(LESpriteinfo)) {
        Sprite sprite=SpriteList.get(i).parse(LESpriteinfo,myGame);
      }
    }
  }
  return field;
}

Fixed version (ground truth):
public PlayField createLevel(String jsonString){
  PlayField field=new PlayField();
  Gson gson=new Gson();
  Scanner scanner;
  try {
    scanner=new Scanner(new File(jsonString));
    String wholeFile=scanner.useDelimiter("String_Node_Str").next();
    Type collectionType=new TypeToken<GameFile>(){
    }
.getType();
    myGameInfo=gson.fromJson(wholeFile,collectionType);
  }
 catch (  FileNotFoundException e) {
    e.printStackTrace();
  }
  if (myGameInfo == null) {
    return null;
  }
  File backgroundPathFile=null;
  BufferedImage myBackground=null;
  try {
    backgroundPathFile=new File(myGameInfo.getBackground());
    myBackground=ImageIO.read(backgroundPathFile);
  }
 catch (  IOException e1) {
    System.out.print("String_Node_Str");
  }
  background=new ImageBackground(myBackground);
  field=new PlayField(background);
  myGame.CHARACTER=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.PROJECTILE=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.POWER_UP=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.PLATFORM=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.SPAWNPOINT=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.COINS=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.BAD_GUYS=field.addGroup(new SpriteGroup("String_Node_Str"));
  myGame.INTERACTIVE_SPRITES=field.addGroup(new SpriteGroup("String_Node_Str"));
  ArrayList<LESprite> SpriteList=new ArrayList<LESprite>();
  SpriteList.add(new Bad_Guys());
  SpriteList.add(new Character());
  SpriteList.add(new Platform());
  for (int k=0; k < myGameInfo.getList().size(); k++) {
    ArrayList<String> LESpriteinfo=myGameInfo.getList().get(k);
    for (int i=0; i < SpriteList.size(); i++) {
      if (SpriteList.get(i).isInstanceOf(LESpriteinfo)) {
        Sprite sprite=SpriteList.get(i).parse(LESpriteinfo,myGame);
      }
    }
  }
  return field;
}