从二叉搜索树递归构建数组时出现Java StackOverflowError

我有:

 public void toArray(E[] a) {
  toArray(root, a, 0);
 }

 /*
  * Adds all elements from the tree rooted at n in inorder to the array a
  * starting at a[index].
  * Returns the index of the last inserted element + 1 (the first empty
  * position in a).
  */
 private int toArray(BinaryNode<E> node, E[] a, int index) {
  if (node.left != null) {
   index = toArray(node, a, index);
  }

  a[index] = node.element;
  index++;

  if (node.right != null) {
   index = toArray(node, a, index);
  }

  return index;
 }

以及:

bst.toArray(b);

我希望这能建立一个有序的数组。但我有StackOverflower错误。据我所知,这可能是由于无限递归,但我真的看不到它。

错误发生在这一行:

index = toArray(node, a, index);