Upstream cannot be null error in APIcast logs

When performing a request the APIcast logs shows the following warning:

2020/05/14 11:32:20 [warn] 18#18: *1434 [lua] apicast.lua:65: upstream api for the service:2 is invalid, error:Upstream cannot be null, client: XX.XXX.X., server: _, request: "GET /abc/api/hello?user_key=<key> HTTP/1.1", host: "api-3scale-apicast-staging.apps.avilatustest.lab.upshift.rdu2.redhat.com"

The warning can be seen for successful requests as well as for failed requests.

The request is to remove this log since it is confusing.

IMPORTANT NOTE: This log message can be ignored as it is not the result of any erroneous behaviour and doesn't change the expected behaviour of the gateway. It only causes confusion and nothing more which is why it is logged as the warn level instead of error.