Program: 49949
Project: 49949
Buggy source:
/** 
 * In this case, only pawns can promote, allow the user to pick which class it promotes to.
 * @param p The piece to promote
 * @param verified Whether it has been verified that thisis ok
 * @param promo What the piece was promoted to.
 * @return The promoted Piece.
 */
public Piece classicPromotion(Piece p,boolean verified,String promo){
  System.out.println(verified);
  if (!verified) {
    lastPromoted=p.getName();
    klazz=p.getName();
  }
  if (verified && promo != null && !promo.equals(p.getName())) {
    System.out.println("String_Node_Str" + promo + "String_Node_Str"+ p.getName());
    try {
      Piece promoted=PieceBuilder.makePiece(promo,p.isBlack(),p.getSquare(),p.getBoard());
      if (promoted.isBlack()) {
        g.getBlackTeam().set(g.getBlackTeam().indexOf(p),promoted);
      }
 else {
        g.getWhiteTeam().set(g.getWhiteTeam().indexOf(p),promoted);
      }
      promoted.getLegalDests().clear();
      promoted.setMoveCount(p.getMoveCount());
      return promoted;
    }
 catch (    Exception e) {
      e.printStackTrace();
    }
  }
  System.out.println("String_Node_Str" + klazz);
  if (!verified && (p.getPromotesTo() == null || p.getPromotesTo().size() == 0))   return p;
  if (!verified && promo == null && g.isBlackMove() == p.isBlack()) {
    klazz="String_Node_Str";
    if (p.getPromotesTo().size() == 1)     klazz=p.getPromotesTo().get(0);
    while (klazz.equals("String_Node_Str")) {
      System.out.println(promo == null);
      String result=(String)JOptionPane.showInputDialog(null,"String_Node_Str","String_Node_Str",JOptionPane.PLAIN_MESSAGE,null,p.getPromotesTo().toArray(),null);
      if (result == null) {
        continue;
      }
      klazz=result;
      promo=result;
    }
  }
 else   if (promo != null && p.getPromotesTo().contains(promo)) {
    klazz=promo;
  }
  try {
    Piece promoted=PieceBuilder.makePiece(klazz,p.isBlack(),p.getSquare(),p.getBoard());
    if (promoted.isBlack()) {
      g.getBlackTeam().set(g.getBlackTeam().indexOf(p),promoted);
    }
 else {
      g.getWhiteTeam().set(g.getWhiteTeam().indexOf(p),promoted);
    }
    promoted.getLegalDests().clear();
    promoted.setMoveCount(p.getMoveCount());
    return promoted;
  }
 catch (  Exception e) {
    e.printStackTrace();
  }
  return null;
}

Fixed version (ground truth):
/** 
 * In this case, only pawns can promote, allow the user to pick which class it promotes to.
 * @param p The piece to promote
 * @param verified Whether it has been verified that thisis ok
 * @param promo What the piece was promoted to.
 * @return The promoted Piece.
 */
public Piece classicPromotion(Piece p,boolean verified,String promo){
  if (p.getPromotesTo() == null || p.getPromotesTo().size() == 0)   return p;
  if (!verified) {
    lastPromoted=p.getName();
    klazz=p.getName();
  }
  if (verified && promo != null && !promo.equals(p.getName())) {
    try {
      Piece promoted=PieceBuilder.makePiece(promo,p.isBlack(),p.getSquare(),p.getBoard());
      if (promoted.isBlack()) {
        g.getBlackTeam().set(g.getBlackTeam().indexOf(p),promoted);
      }
 else {
        g.getWhiteTeam().set(g.getWhiteTeam().indexOf(p),promoted);
      }
      promoted.getLegalDests().clear();
      promoted.setMoveCount(p.getMoveCount());
      return promoted;
    }
 catch (    Exception e) {
      e.printStackTrace();
    }
  }
  System.out.println("String_Node_Str" + klazz);
  if (!verified && (p.getPromotesTo() == null || p.getPromotesTo().size() == 0))   return p;
  if (!verified && promo == null && g.isBlackMove() == p.isBlack()) {
    klazz="String_Node_Str";
    if (p.getPromotesTo().size() == 1)     klazz=p.getPromotesTo().get(0);
    while (klazz.equals("String_Node_Str")) {
      System.out.println(promo == null);
      String result=(String)JOptionPane.showInputDialog(null,"String_Node_Str","String_Node_Str",JOptionPane.PLAIN_MESSAGE,null,p.getPromotesTo().toArray(),null);
      if (result == null) {
        continue;
      }
      klazz=result;
      promo=result;
    }
  }
 else   if (promo != null && p.getPromotesTo() != null && p.getPromotesTo().contains(promo)) {
    klazz=promo;
  }
  try {
    Piece promoted=PieceBuilder.makePiece(klazz,p.isBlack(),p.getSquare(),p.getBoard());
    if (promoted.isBlack()) {
      g.getBlackTeam().set(g.getBlackTeam().indexOf(p),promoted);
    }
 else {
      g.getWhiteTeam().set(g.getWhiteTeam().indexOf(p),promoted);
    }
    promoted.getLegalDests().clear();
    promoted.setMoveCount(p.getMoveCount());
    return promoted;
  }
 catch (  Exception e) {
    e.printStackTrace();
  }
  return null;
}