Incorrect attribute access causing response middleware errors

[john-g-g]

if request.method == 'POST' and isinstance(request.json, JussiJSONRPCRequest):
will, in some circumstances produce this error:

{
  "event": "finalize_jussi error",
  "logger": "jussi.middlewares.jussi",
  "level": "warning",
  "exception": "Traceback (most recent call last):\n 
File \"/app/.venv/lib/python3.6/site-packages/sanic/request.py\", line 89, in load_json\n self.parsed_json = loads(self.body)\n
ValueError: Expected object or value\n\n
During handling of the above exception, another exception occurred:\n\nTraceback (most recent call last):\n 
File \"/app/jussi/middlewares/jussi.py\", line 56, in finalize_jussi_response\n 
if request.method == POST and isinstance(request.json, JussiJSONRPCRequest):\n 
File \"/app/.venv/lib/python3.6/site-packages/sanic/request.py\", line 83, in json\n
self.load_json()\n 
File \"/app/.venv/lib/python3.6/site-packages/sanic/request.py\", line 93, in load_json\n 
raise InvalidUsage(\"Failed when parsing body as json\")\n
sanic.exceptions.InvalidUsage: Failed when parsing body as json"
}