Program: 157787
Project: 157787
Buggy source:
@SuppressWarnings({"String_Node_Str","String_Node_Str"}) private int doDamage(int damage,UUID sourceId,Game game,boolean combatDamage,boolean preventable,List<UUID> appliedEffects){
  if (damage > 0) {
    if (canDamage(game.getObject(sourceId),game)) {
      GameEvent event=new DamagePlayerEvent(playerId,sourceId,playerId,damage,preventable,combatDamage);
      event.setAppliedEffects(appliedEffects);
      if (!game.replaceEvent(event)) {
        int actualDamage=event.getAmount();
        if (actualDamage > 0) {
          UUID sourceControllerId=null;
          Abilities sourceAbilities=null;
          MageObject source=game.getPermanentOrLKIBattlefield(sourceId);
          if (source == null) {
            StackObject stackObject=game.getStack().getStackObject(sourceId);
            if (stackObject != null) {
              source=stackObject.getStackAbility().getSourceObject(game);
            }
 else {
              source=game.getObject(sourceId);
            }
            if (source instanceof Spell) {
              sourceAbilities=((Spell)source).getAbilities(game);
              sourceControllerId=((Spell)source).getControllerId();
            }
 else             if (source instanceof Card) {
              sourceAbilities=((Card)source).getAbilities(game);
              sourceControllerId=((Card)source).getOwnerId();
            }
 else             if (source instanceof CommandObject) {
              sourceControllerId=((CommandObject)source).getControllerId();
              sourceAbilities=((CommandObject)source).getAbilities();
            }
          }
 else {
            sourceAbilities=((Permanent)source).getAbilities(game);
            sourceControllerId=((Permanent)source).getControllerId();
          }
          if (sourceAbilities != null && sourceAbilities.containsKey(InfectAbility.getInstance().getId())) {
            addCounters(CounterType.POISON.createInstance(actualDamage),game);
          }
 else {
            GameEvent damageToLifeLossEvent=new GameEvent(EventType.DAMAGE_CAUSES_LIFE_LOSS,playerId,sourceId,playerId,actualDamage,combatDamage);
            if (!game.replaceEvent(damageToLifeLossEvent)) {
              this.loseLife(damageToLifeLossEvent.getAmount(),game,combatDamage);
            }
          }
          if (sourceAbilities != null && sourceAbilities.containsKey(LifelinkAbility.getInstance().getId())) {
            Player player=game.getPlayer(sourceControllerId);
            player.gainLife(actualDamage,game);
          }
          if (sourceAbilities.containsKey(SquirrellinkAbility.getInstance().getId())) {
            Player player=game.getPlayer(sourceControllerId);
            new SquirrelToken().putOntoBattlefield(actualDamage,game,sourceId,player.getId());
          }
          game.fireEvent(new DamagedPlayerEvent(playerId,sourceId,playerId,actualDamage,combatDamage));
          return actualDamage;
        }
      }
    }
 else {
      MageObject sourceObject=game.getObject(sourceId);
      game.informPlayers(damage + "String_Node_Str" + (sourceObject == null ? "String_Node_Str" : "String_Node_Str" + sourceObject.getLogName())+ "String_Node_Str"+ getLogName()+ (damage > 1 ? "String_Node_Str" : "String_Node_Str")+ "String_Node_Str");
    }
  }
  return 0;
}

Fixed version (ground truth):
@SuppressWarnings({"String_Node_Str","String_Node_Str"}) private int doDamage(int damage,UUID sourceId,Game game,boolean combatDamage,boolean preventable,List<UUID> appliedEffects){
  if (damage > 0) {
    if (canDamage(game.getObject(sourceId),game)) {
      GameEvent event=new DamagePlayerEvent(playerId,sourceId,playerId,damage,preventable,combatDamage);
      event.setAppliedEffects(appliedEffects);
      if (!game.replaceEvent(event)) {
        int actualDamage=event.getAmount();
        if (actualDamage > 0) {
          UUID sourceControllerId=null;
          Abilities sourceAbilities=null;
          MageObject source=game.getPermanentOrLKIBattlefield(sourceId);
          if (source == null) {
            StackObject stackObject=game.getStack().getStackObject(sourceId);
            if (stackObject != null) {
              source=stackObject.getStackAbility().getSourceObject(game);
            }
 else {
              source=game.getObject(sourceId);
            }
            if (source instanceof Spell) {
              sourceAbilities=((Spell)source).getAbilities(game);
              sourceControllerId=((Spell)source).getControllerId();
            }
 else             if (source instanceof Card) {
              sourceAbilities=((Card)source).getAbilities(game);
              sourceControllerId=((Card)source).getOwnerId();
            }
 else             if (source instanceof CommandObject) {
              sourceControllerId=((CommandObject)source).getControllerId();
              sourceAbilities=((CommandObject)source).getAbilities();
            }
          }
 else {
            sourceAbilities=((Permanent)source).getAbilities(game);
            sourceControllerId=((Permanent)source).getControllerId();
          }
          if (sourceAbilities != null && sourceAbilities.containsKey(InfectAbility.getInstance().getId())) {
            addCounters(CounterType.POISON.createInstance(actualDamage),game);
          }
 else {
            GameEvent damageToLifeLossEvent=new GameEvent(EventType.DAMAGE_CAUSES_LIFE_LOSS,playerId,sourceId,playerId,actualDamage,combatDamage);
            if (!game.replaceEvent(damageToLifeLossEvent)) {
              this.loseLife(damageToLifeLossEvent.getAmount(),game,combatDamage);
            }
          }
          if (sourceAbilities != null && sourceAbilities.containsKey(LifelinkAbility.getInstance().getId())) {
            Player player=game.getPlayer(sourceControllerId);
            player.gainLife(actualDamage,game);
          }
          if (sourceAbilities != null && sourceAbilities.containsKey(SquirrellinkAbility.getInstance().getId())) {
            Player player=game.getPlayer(sourceControllerId);
            new SquirrelToken().putOntoBattlefield(actualDamage,game,sourceId,player.getId());
          }
          game.fireEvent(new DamagedPlayerEvent(playerId,sourceId,playerId,actualDamage,combatDamage));
          return actualDamage;
        }
      }
    }
 else {
      MageObject sourceObject=game.getObject(sourceId);
      game.informPlayers(damage + "String_Node_Str" + (sourceObject == null ? "String_Node_Str" : "String_Node_Str" + sourceObject.getLogName())+ "String_Node_Str"+ getLogName()+ (damage > 1 ? "String_Node_Str" : "String_Node_Str")+ "String_Node_Str");
    }
  }
  return 0;
}