我得到的错误是：
"无法将参数类型" TextSpan "赋给参数类型" List？"
下面是代码：

Widget buildSignUpBtn() {
    return GestureDetector(
      onTap: () => print('SignUp Pressed'),
      child: RichText(
        text: TextSpan(
          children: TextSpan(
            text: 'Don\'t have an Account',
            style: TextStyle(
              color: Colors.white,
              fontSize: 18.0,
              fontWeight: FontWeight.w500,
            ),
          ),
          TextSpan(
            text: 'Don\'t have an Account',
            style: TextStyle(
              color: Colors.white,
              fontSize: 18.0,
              fontWeight: FontWeight.w500,
            ),
          ),
        ),
      ),
    );
  }

请帮我解决这个问题!