NoneType is not iterable (finish_response)

[speccy88]

Can anyone tell me what could cause this error?
Traceback (most recent call last): File "code.py", line 107, in <module> File "adafruit_esp32spi/adafruit_esp32spi_wsgiserver.py", line 106, in update_poll File "adafruit_esp32spi/adafruit_esp32spi_wsgiserver.py", line 122, in finish_response TypeError: 'NoneType' object is not iterable

[mfinkle]

I have run into this kind of error when I forget to add a return to my route handlers. Make sure you add the final line:

@web_app.route("/led_on/<r>/<g>/<b>")
def led_on(request, r, g, b): 
    print("led on!")
    status_light.fill((int(r), int(g), int(b)))
    return ("200 OK", [], [])

Even when you are handling a POST:

@web_app.route("/led_on", ["POST"])
def led_on(request):
    print("led on!")
    r = request.query_params["r"]
    g = request.query_params["g"]
    b = request.query_params["b"]
    status_light.fill((int(r), int(g), int(b)))
    return ("200 OK", [], [])

The third parameter is the response content and it needs to be iterable, like an empty List, or even an empty string.