Tidy message returned when specifying invalid PolicyData

[donaldgray]

Posting invalid policyData value when managing DeliveryChannelPolicy results in a 400 being returned but the error message contains unexpected values "" and "hydraDeliveryChannelPolicy" properties.

e.g. using "policyData": ["200,"] returned:

{
    "errors": {
        "": [
            "JsonToken EndArray is not valid for closing JsonType Object. Path '', line 4, position 24."
        ],
        "policyData": [
            "Unexpected character encountered while parsing value: [. Path 'policyData', line 4, position 17."
        ],
        "hydraDeliveryChannelPolicy": [
            "The hydraDeliveryChannelPolicy field is required."
        ]
    },
    "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
    "title": "One or more validation errors occurred.",
    "status": 400,
    "traceId": "00-8491ee7970f67dbfb62a7dfe2d9fff53-73f594eb3b28831c-00"
}

[donaldgray]

Parking for now, issue with "" property seems to be related to general deserialization issue when model given incorrect type.