public @Nullable ASTNode findChildByRole(int role) {
    // assert ChildRole.isUnique(role);
    for (ASTNode child = getFirstChildNode(); child != null; child = child.getTreeNext()) {
      if (getChildRole(child) == role) return child;
    }
    return null;
  }
public @Nullable ASTNode findChildByRole(int role)