Exporters/Prometheus: Unable to record metrics

[PikBot]

On running the following code, I get the following error:

Exception happened during processing of request from ('127.0.0.1', 50691)
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/socketserver.py", line 625, in process_request_thread
    self.finish_request(request, client_address)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/socketserver.py", line 354, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/socketserver.py", line 681, in __init__
    self.handle()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/server.py", line 422, in handle
    self.handle_one_request()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/server.py", line 410, in handle_one_request
    method()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/prometheus_client/exposition.py", line 146, in do_GET
    output = encoder(registry)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/prometheus_client/openmetrics/exposition.py", line 26, in generate_latest
    for k, v in sorted(s.labels.items())]))
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/prometheus_client/openmetrics/exposition.py", line 26, in <listcomp>
    for k, v in sorted(s.labels.items())]))
AttributeError: 'NoneType' object has no attribute 'replace'

I have tried running the example for Prometheus exporter as well (that doesn't seem to work for me either).
Not sure whether it is related to this?
Any suggestions on as to what could be wrong, would be helpful!
@odeke-em

[songy23]

Seems Prometheus doesn't allow label values to be None. Sending a PR to fix soon.

[PikBot]

Thank you @songy23 !