private void printTree(StringBuilder builder, int nestingLevel) {
    for (int i = 0; i < nestingLevel; i++) builder.append("  ");
    builder.append(this).append('\n');
    for (StubElement<?> child : getChildrenStubs()) {
      ((StubBase<?>)child).printTree(builder, nestingLevel + 1);
    }
  }
private void printTree(StringBuilder builder, int nestingLevel)