在async Select组件中添加isLoading和options属性，当isLoading为true时显示loading动画，当options为空时不显示下拉菜单。

示例代码：

import React, { useState } from "react";
import AsyncSelect from "react-select/async";
import { fetchOptions } from "./api";

function MyAsyncSelect() {
  const [options, setOptions] = useState([]);
  const [isLoading, setIsLoading] = useState(false);

  const loadOptions = async (inputValue) => {
    setIsLoading(true);
    const data = await fetchOptions(inputValue);
    setOptions(data);
    setIsLoading(false);
  };

  return (
     "无匹配项"}
    />
  );
}

export default MyAsyncSelect;