promgen: Cannot use TestQuery function

Hi Team, I tried to install Promgen via docker-compose and manual as well. Anyway, In both of way, I can not use TestQuery function. It always show jquery.min.js:4 POST http://127.0.0.1:8080/rule/0/test 500 (Internal Server Error)

Log file from docker-compose

> web_1           | [02/Aug/2019 06:25:32] "POST /rule/0/test HTTP/1.1" 500 16836
web_1           | Internal Server Error: /rule/0/test
web_1           | Traceback (most recent call last):
web_1           |   File "/usr/local/lib/python3.6/site-packages/django/core/handlers/exception.py", line 34, in inner
web_1           |     response = get_response(request)
web_1           |   File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py", line 115, in _get_response
web_1           |     response = self.process_exception_by_middleware(e, request)
web_1           |   File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py", line 113, in _get_response
web_1           |     response = wrapped_callback(request, *callback_args, **callback_kwargs)
web_1           |   File "/usr/local/lib/python3.6/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
web_1           |     return view_func(*args, **kwargs)
web_1           |   File "/usr/local/lib/python3.6/site-packages/django/views/generic/base.py", line 71, in view
web_1           |     return self.dispatch(request, *args, **kwargs)
web_1           |   File "/usr/local/lib/python3.6/site-packages/django/contrib/auth/mixins.py", line 52, in dispatch
web_1           |     return super().dispatch(request, *args, **kwargs)
web_1           |   File "/usr/local/lib/python3.6/site-packages/django/views/generic/base.py", line 97, in dispatch
web_1           |     return handler(request, *args, **kwargs)
web_1           |   File "/usr/src/app/promgen/views.py", line 1241, in post
web_1           |     result = util.get(url, {'query': query}).json()
web_1           |   File "/usr/local/lib/python3.6/site-packages/requests/models.py", line 897, in json
web_1           |     return complexjson.loads(self.text, **kwargs)
web_1           |   File "/usr/local/lib/python3.6/json/__init__.py", line 354, in loads
web_1           |     return _default_decoder.decode(s)
web_1           |   File "/usr/local/lib/python3.6/json/decoder.py", line 339, in decode
web_1           |     obj, end = self.raw_decode(s, idx=_w(s, 0).end())
web_1           |   File "/usr/local/lib/python3.6/json/decoder.py", line 357, in raw_decode
web_1           |     raise JSONDecodeError("Expecting value", s, err.value) from None
web_1           | json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)`

Can you have a look? Thank you CC: @kfdm