FlatteningDeSerializer fails to deserialize objects only containing "@odata.type" field

[crachmanin]

When attempting to deserialize a json object only containing a type discriminator, the FlatteningDeserializer fails with the following error:

Cannot deserialize instance of <OBJECT_NAME> out of VALUE_NULL token

So when attempting to deserialize the following string

{
    "name": "SharedContentKeyPolicyUsedByAllAssets2",
    "id": "/subscriptions/b2c12710-ecdf-4532-9ba6-7e74a219b5f2/resourceGroups/mpusw2/providers/Microsoft.Media/mediaservices/krishndurpv3/contentKeyPolicies/SharedContentKeyPolicyUsedByAllAssets2",
    "type": "Microsoft.Media/mediaservices/contentKeyPolicies",
    "properties": {
        "policyId": "5a662975-4918-4c6d-a595-01e08330f5f2",
        "created": "2019-05-22T21:47:22.427Z",
        "lastModified": "2019-05-23T01:01:22.497Z",
        "options": [
            {
                "policyOptionId": "eff2f987-2251-40ee-a5b9-f9baba86595b",
                "configuration": {
                    "@odata.type": "#Microsoft.Media.ContentKeyPolicyClearKeyConfiguration"
                },
                "restriction": {
                    "@odata.type": "#Microsoft.Media.ContentKeyPolicyTokenRestriction",
                    "issuer": "myIssuer",
                    "audience": "myAudience",
                    "primaryVerificationKey": {
                        "@odata.type": "#Microsoft.Media.ContentKeyPolicySymmetricTokenKey"
                    },
                    "alternateVerificationKeys": [],
                    "requiredClaims": [
                        {
                            "claimType": "urn:microsoft:azure:mediaservices:contentkeyidentifier"
                        }
                    ],
                    "restrictionTokenType": "Jwt"
                }
            }
        ]
    }
}

The following error occurs:
Cannot deserialize instance of com.microsoft.azure.management.mediaservices.v2018_07_01.ContentKeyPolicyClearKeyConfiguration out of VALUE_NULL token

Since the configuration object only contains the type discriminator.

If I modify the json while debugging so that there is an additional field:

"configuration": {
                    "@odata.type": "#Microsoft.Media.ContentKeyPolicyClearKeyConfiguration",
                    "test_data": "test"
                 }

The deserialization is successful.

This issue prevent users from creating ContentKeyPolicy objects using the Java SDK generated for Azure Media Services (see https://github.com/Azure/azure-sdk-for-java/tree/master/mediaservices/resource-manager/v2018_07_01 beta 3 version)