When a  service-type has no service-instance, service inventory find returns empty.

Example:

"service-subscription": [

            {

                "service-type": "network_test",

                "resource-version": "1524672896268"

            },

            {

                "service-type": "vPCRF",

                "resource-version": "1524083801352",

                "service-instances": {

                    "service-instance": [

                        {

                            "service-instance-id": "39ff3f9d-f210-4566-9d19-fa37edf1697d",

                            "service-instance-name": "vPCRF",

                            "model-invariant-id": "a09e799f-58eb-4c00-bfcc-4fa371a557e3",

                            "model-version-id": "4c393977-09ea-42c2-bcd9-f50302ebba48",

                            "resource-version": "1524672125232"

                        }

                    ]

                },