python3 AttributeError: 'NoneType' object has no attribute 'split'

from wsgiref.simple_server import make_server
 
def RunServer(environ, start_response):
    start_response('200 ok',[('Content-Type','text/html')])
    return '<h1>Hello world</h1>'

if __name__ == '__main__':
    httpd = make_server('127.0.0.1',9000,RunServer)
    print('servering HTTP on port 9000')
    httpd.serve_forever()

运行时报错：

self.status.split(' ',1)[0], self.bytes_sent
AttributeError: 'NoneType' object has no attribute 'split'

解决办法如下：

return ['<h1>Hello world</h1>'.encode('utf-8'),]