Program: 59245
Project: 59245
Buggy source:
/** 
 * FOR INTERNAL USE ONLY.  Aligned merge two sets of aggregaets...possibly modifying one of them. Can only be used if BOTH sets of aggregates are only held in the current scope AND going out of scope immediately after the merge.   Combine two aggregate sets according to the passed reducer.  Aligns coordinates between the two sets.  The resulting aggregate set will have a realized subset region sufficient to cover the realized subset region of both source aggregate sets (regardless of  the values found in those sources).  If one of the two aggregate sets provided is already of sufficient size, it will be used as both a source and a target. Therefore, this may involve a **DESTRUCTIVE** update of one of the sets of aggregates.
 * @param left Aggregate set to use for left-hand arguments
 * @param right Aggregate set to use for right-hand arguments
 * @param identity Identity value for the rollup function
 * @param rollup Reduction operation
 * @return Resulting aggregate set (may be new or a destructively updated left or right parameter) 
 */
public static <T>Aggregates<T> __unsafeMerge(Aggregates<T> left,Aggregates<T> right,T identity,BiFunction<T,T,T> rollup){
  if (left == null || left.empty()) {
    return right;
  }
  if (right == null || right.empty()) {
    return left;
  }
  if ((left instanceof ConstantAggregates) && Util.isEqual(identity,left.defaultValue())) {
    return right;
  }
  if ((right instanceof ConstantAggregates) && Util.isEqual(identity,right.defaultValue())) {
    return left;
  }
  List<Aggregates<T>> sources=new ArrayList<Aggregates<T>>();
  Aggregates<T> target;
  Rectangle rb=new Rectangle(right.lowX(),right.lowY(),right.highX() - right.lowX(),right.highY() - right.lowY());
  Rectangle lb=new Rectangle(left.lowX(),left.lowY(),left.highX() - left.lowX(),left.highY() - left.lowY());
  Rectangle bounds=rb.union(lb);
  if (lb.contains(bounds)) {
    target=left;
    sources.add(right);
  }
 else   if (rb.contains(bounds)) {
    target=right;
    sources.add(left);
  }
 else {
    sources.add(left);
    sources.add(right);
    target=AggregateUtils.make((int)bounds.getMinX(),(int)bounds.getMinY(),(int)bounds.getMaxX(),(int)bounds.getMaxY(),identity);
  }
  for (  Aggregates<T> source : sources) {
    for (int x=Math.max(0,source.lowX()); x < source.highX(); x++) {
      for (int y=Math.max(0,source.lowY()); y < source.highY(); y++) {
        T newVal=source.get(x,y);
        if (Util.isEqual(identity,newVal)) {
          continue;
        }
        T comb=rollup.apply(target.get(x,y),source.get(x,y));
        target.set(x,y,comb);
      }
    }
  }
  return target;
}

Fixed version (ground truth):
/** 
 * FOR INTERNAL USE ONLY.  Aligned merge two sets of aggregaets...possibly modifying one of them. Can only be used if BOTH sets of aggregates are only held in the current scope AND going out of scope immediately after the merge.   Combine two aggregate sets according to the passed reducer.  Aligns coordinates between the two sets.  The resulting aggregate set will have a realized subset region sufficient to cover the realized subset region of both source aggregate sets (regardless of  the values found in those sources).  If one of the two aggregate sets provided is already of sufficient size, it will be used as both a source and a target. Therefore, this may involve a **DESTRUCTIVE** update of one of the sets of aggregates.
 * @param left Aggregate set to use for left-hand arguments
 * @param right Aggregate set to use for right-hand arguments
 * @param identity Identity value for the rollup function
 * @param rollup Reduction operation
 * @return Resulting aggregate set (may be new or a destructively updated left or right parameter) 
 */
public static <T>Aggregates<T> __unsafeMerge(Aggregates<T> left,Aggregates<T> right,T identity,BiFunction<T,T,T> rollup){
  if (left == null || left.empty()) {
    return right;
  }
  if (right == null || right.empty()) {
    return left;
  }
  if ((left instanceof ConstantAggregates) && Util.isEqual(identity,left.defaultValue())) {
    return right;
  }
  if ((right instanceof ConstantAggregates) && Util.isEqual(identity,right.defaultValue())) {
    return left;
  }
  List<Aggregates<T>> sources=new ArrayList<Aggregates<T>>();
  Aggregates<T> target;
  Rectangle rb=new Rectangle(right.lowX(),right.lowY(),right.highX() - right.lowX(),right.highY() - right.lowY());
  Rectangle lb=new Rectangle(left.lowX(),left.lowY(),left.highX() - left.lowX(),left.highY() - left.lowY());
  Rectangle bounds=rb.union(lb);
  if (lb.contains(bounds)) {
    target=left;
    sources.add(right);
  }
 else   if (rb.contains(bounds)) {
    target=right;
    sources.add(left);
  }
 else {
    sources.add(left);
    sources.add(right);
    target=AggregateUtils.make((int)bounds.getMinX(),(int)bounds.getMinY(),(int)bounds.getMaxX(),(int)bounds.getMaxY(),identity);
  }
  for (  Aggregates<T> source : sources) {
    for (int x=source.lowX(); x < source.highX(); x++) {
      for (int y=source.lowY(); y < source.highY(); y++) {
        T newVal=source.get(x,y);
        if (Util.isEqual(identity,newVal)) {
          continue;
        }
        T comb=rollup.apply(target.get(x,y),source.get(x,y));
        target.set(x,y,comb);
      }
    }
  }
  return target;
}