query_params is NoneType if URL contains parameters

The following example called with `http:///api/sensor1?property=tempurature` fails with `AttributeError: 'NoneType' object has no attribute 'get'` when calling get on `query_params`

```
@app.route("/{sensor}", methods=["POST", "GET"], content_types=["application/json"])
def sensor_info(sensor):
if app.current_request.method == "GET":
property = app.current_request.query_params.get("property", None)
res = some_db_query()
return res
```

Perhaps I am missing something, but from the examples I have seen, this should work as expected (i.e. query_params should exist).