Program: 101023
Project: 101023
Buggy source:
@SuppressWarnings("String_Node_Str") private T insert(MapNode<T> node,char[] letters,int offset,T value){
  int lettersRest=letters.length - offset;
  while (true) {
    int thisLettersLength=node.getLetters().length;
    int n=Math.min(lettersRest,thisLettersLength);
    int i=0;
    while (i < n && (letters[i + offset] - node.getLetters()[i]) == 0)     i++;
    if (i != n) {
      MapNode<T> child1=new MapNode<T>(Arrays.copyOfRange(node.getLetters(),i,node.getLetters().length),node.isTerminate(),node.getChildren(),((MapNode<T>)node).getValue());
      MapNode<T> child2=new MapNode<T>(Arrays.copyOfRange(letters,i + offset,letters.length),true,value);
      node.setLetters(Arrays.copyOfRange(node.getLetters(),0,i));
      node.setTerminate(false);
      node.setChildren((child1.getLetters()[0] < child2.getLetters()[0]) ? new Node[]{child1,child2} : new Node[]{child2,child1});
      node.setValue(null);
      size++;
    }
 else     if (lettersRest == thisLettersLength) {
      if (!node.isTerminate()) {
        node.setTerminate(true);
        size++;
      }
      MapNode<T> mn=(MapNode<T>)node;
      T old=mn.getValue();
      mn.setValue(value);
      return old;
    }
 else     if (lettersRest < thisLettersLength) {
      MapNode<T> newChild=new MapNode<T>(Arrays.copyOfRange(node.getLetters(),lettersRest,thisLettersLength),node.isTerminate(),node.getChildren());
      newChild.setValue(((MapNode<T>)node).getValue());
      node.setLetters(Arrays.copyOfRange(node.getLetters(),0,i));
      node.setTerminate(true);
      node.setChildren(new Node[]{newChild});
      ((MapNode<T>)node).setValue(value);
      size++;
    }
 else {
      int index=0;
      int end=node.getChildren().length;
      boolean cont=false;
      if (end > 16) {
        int start=0;
        while (start < end) {
          index=(start + end) / 2;
          MapNode<T> child=node.getChildren()[index];
          int c=letters[i + offset] - child.getLetters()[0];
          if (c == 0) {
            node=child;
            offset+=i;
            lettersRest-=i;
            cont=true;
            break;
          }
          if (c < 0) {
            end=index;
          }
 else           if (start == index) {
            index=end;
            break;
          }
 else {
            start=index;
          }
        }
      }
 else {
        for (; index < end; index++) {
          MapNode<T> child=node.getChildren()[index];
          int c=letters[i + offset] - child.getLetters()[0];
          if (c < 0)           break;
          if (c == 0) {
            node=child;
            offset+=i;
            lettersRest-=i;
            cont=true;
            break;
          }
        }
      }
      if (cont)       continue;
      node.addChild(index,new MapNode<T>(Arrays.copyOfRange(letters,i + offset,letters.length),true,value));
      size++;
    }
    break;
  }
  return null;
}

Fixed version (ground truth):
@SuppressWarnings("String_Node_Str") private T insert(MapNode<T> node,char[] letters,int offset,T value){
  int lettersRest=letters.length - offset;
  while (true) {
    int thisLettersLength=node.getLetters().length;
    int n=Math.min(lettersRest,thisLettersLength);
    int i=0;
    while (i < n && (letters[i + offset] - node.getLetters()[i]) == 0)     i++;
    if (i != n) {
      MapNode<T> child1=new MapNode<T>(Arrays.copyOfRange(node.getLetters(),i,node.getLetters().length),node.isTerminate(),node.getChildren(),((MapNode<T>)node).getValue());
      MapNode<T> child2=new MapNode<T>(Arrays.copyOfRange(letters,i + offset,letters.length),true,value);
      node.setLetters(Arrays.copyOfRange(node.getLetters(),0,i));
      node.setTerminate(false);
      node.setChildren((child1.getLetters()[0] < child2.getLetters()[0]) ? new MapNode[]{child1,child2} : new MapNode[]{child2,child1});
      node.setValue(null);
      size++;
    }
 else     if (lettersRest == thisLettersLength) {
      if (!node.isTerminate()) {
        node.setTerminate(true);
        size++;
      }
      T old=node.getValue();
      node.setValue(value);
      return old;
    }
 else     if (lettersRest < thisLettersLength) {
      MapNode<T> newChild=new MapNode<T>(Arrays.copyOfRange(node.getLetters(),lettersRest,thisLettersLength),node.isTerminate(),node.getChildren());
      newChild.setValue(node.getValue());
      node.setLetters(Arrays.copyOfRange(node.getLetters(),0,i));
      node.setTerminate(true);
      node.setChildren(new MapNode[]{newChild});
      node.setValue(value);
      size++;
    }
 else {
      int index=0;
      int end=node.getChildren().length;
      boolean cont=false;
      if (end > 16) {
        int start=0;
        while (start < end) {
          index=(start + end) / 2;
          MapNode<T> child=node.getChildren()[index];
          int c=letters[i + offset] - child.getLetters()[0];
          if (c == 0) {
            node=child;
            offset+=i;
            lettersRest-=i;
            cont=true;
            break;
          }
          if (c < 0) {
            end=index;
          }
 else           if (start == index) {
            index=end;
            break;
          }
 else {
            start=index;
          }
        }
      }
 else {
        for (; index < end; index++) {
          MapNode<T> child=node.getChildren()[index];
          int c=letters[i + offset] - child.getLetters()[0];
          if (c < 0)           break;
          if (c == 0) {
            node=child;
            offset+=i;
            lettersRest-=i;
            cont=true;
            break;
          }
        }
      }
      if (cont)       continue;
      node.addChild(index,new MapNode<T>(Arrays.copyOfRange(letters,i + offset,letters.length),true,value));
      size++;
    }
    break;
  }
  return null;
}