python flask 请求无返回值错误：内部服务器错误

线上报警 5xx 错误，查看日志发现报这个错，

TypeError: The view function did not return a valid response. The function either returned None or ended without a return statement.

这个方法没有有效的返回结果

页面报这个错误

Internal Server Error

The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.

服务器遇到内部错误，无法完成您的请求。服务器过载或应用程序出错。

# flask 请求不可以没有返回值
# The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.
import flask

from flask import Flask, request

app = Flask(__name__)


@app.route('/func')
# 展示数据
def func():
  return  # 这块有问题
# TypeError: The view function did not return a valid response. The function either returned None or ended without a return statement.

if __name__ == "__main__":
    app.run(host='127.0.0.1',port='9090')

修改方法，加个返回值就好了。