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

[PM]

I'm writing very simple code while learning Django. I noticed there is some error in the server console window sometimes when I refreshed my browser.

The error always ends with the line in the ticket Summary. The following is the entire copy of the error.
What the strange is everything works good except the error information. Nothing is broken. The view is always rendered properly. Also, this error doesn't always happen. It occurs occasionally. Any idea of what it means?

[17/Apr/2019 14:52:40] "GET /favicon.ico HTTP/1.1" 404 2189
Traceback (most recent call last):
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 138, in run
    self.finish_response()
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 180, in finish_response
    self.write(data)
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 274, in write
    self.send_headers()
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 332, in send_headers
    self.send_preamble()
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 255, in send_preamble
    ('Date: %s\r\n' % format_date_time(time.time())).encode('iso-8859-1')
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 453, in _write
    result = self.stdout.write(data)
  File "C:\Python\Python37\lib\socketserver.py", line 799, in write
    self._sock.sendall(b)
ConnectionAbortedError: [WinError 10053] An established connection was aborted by the software in your host machine
[17/Apr/2019 14:52:40] "GET /favicon.ico HTTP/1.1" 500 59
----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 55341)
Traceback (most recent call last):
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 138, in run
    self.finish_response()
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 180, in finish_response
    self.write(data)
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 274, in write
    self.send_headers()
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 332, in send_headers
    self.send_preamble()
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 255, in send_preamble
    ('Date: %s\r\n' % format_date_time(time.time())).encode('iso-8859-1')
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 453, in _write
    result = self.stdout.write(data)
  File "C:\Python\Python37\lib\socketserver.py", line 799, in write
    self._sock.sendall(b)
ConnectionAbortedError: [WinError 10053] An established connection was aborted by the software in your host machine

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 141, in run
    self.handle_error()
  File "C:\PythonCode\SeaMotor\venv\lib\site-packages\django\core\servers\basehttp.py", line 116, in handle_error
    super().handle_error()
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 368, in handle_error
    self.finish_response()
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 180, in finish_response
    self.write(data)
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 274, in write
    self.send_headers()
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 331, in send_headers
    if not self.origin_server or self.client_is_modern():
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 344, in client_is_modern
    return self.environ['SERVER_PROTOCOL'].upper() != 'HTTP/0.9'
TypeError: 'NoneType' object is not subscriptable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Python\Python37\lib\socketserver.py", line 650, in process_request_thread
    self.finish_request(request, client_address)
  File "C:\Python\Python37\lib\socketserver.py", line 360, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "C:\Python\Python37\lib\socketserver.py", line 720, in __init__
    self.handle()
  File "C:\PythonCode\SeaMotor\venv\lib\site-packages\django\core\servers\basehttp.py", line 171, in handle
    self.handle_one_request()
  File "C:\PythonCode\SeaMotor\venv\lib\site-packages\django\core\servers\basehttp.py", line 194, in handle_one_request
    handler.run(self.server.get_app())
  File "C:\Python\Python37\lib\wsgiref\handlers.py", line 144, in run
    self.close()
  File "C:\PythonCode\SeaMotor\venv\lib\site-packages\django\core\servers\basehttp.py", line 111, in close
    super().close()
  File "C:\Python\Python37\lib\wsgiref\simple_server.py", line 35, in close
    self.status.split(' ',1)[0], self.bytes_sent
AttributeError: 'NoneType' object has no attribute 'split'

[Mariusz Felisiak]

Duplicate of #30377.

[linehammer]

The AttributeError is an exception thrown when an object does not have the attribute you tried to access. 'NoneType' object has no attribute 'split' often indicates that the attribute you are trying to split is Null, meaning there is no value in it to ​split. So, you need to check the attribute is not Null before splitting. Something like..

if val is not None:

# ...