BatchResponseContent fails when processing "error": null in batch responses

Description

The SDK throws IllegalStateException while processing batch responses when the body.error field is explicitly present but set to null.

The following exception is thrown:

java.lang.IllegalStateException: Not a JSON Object: null
    at com.google.gson.JsonElement.getAsJsonObject(JsonElement.java:91)
    at com.microsoft.graph.core.content.BatchResponseContent.getResponseFromJsonObject(BatchResponseContent.java:199)

Expected behavior

The SDK should ignore error: null and correctly process value.

How to reproduce

Create a batch request with a countIf operation in Microsoft Graph java SDK.

public void countIf(String driveId, String itemId, String criteria, String range) throws IOException {
  // Construct the CountIfPostRequestBody

CountIfPostRequestBody countIfPostRequestBody = new CountIfPostRequestBody();

countIfPostRequestBody.setCriteria(new UntypedString(criteria));
countIfPostRequestBody.setRange(new UntypedObject(Map.of("Address", new UntypedString(range))));

// Call the Graph API

RequestInformation postRequestInformation = graphServiceClient
        .drives()
        .byDriveId(driveId)
        .items()
        .byDriveItemId(itemId)
        .workbook()
        .functions()
        .countIf()
        .toPostRequestInformation(countIfPostRequestBody);


BatchRequestContent batchRequestContent = new BatchRequestContent(graphServiceClient);


String requestId = batchRequestContent.addBatchRequestStep(postRequestInformation);

BatchResponseContent batchResponseContent =
        graphServiceClient.getBatchRequestBuilder().post(batchRequestContent, null);

Response response = batchResponseContent.getResponseById(requestId);

}

Microsoft Graph API returns a valid batch response like this:

{
    "responses": [
        {
            "id": "countIfRequest",
            "status": 200,
            "body": {
                "@odata.context": "https://graph.microsoft.com/v1.0/$metadata#microsoft.graph.workbookFunctionResult",
                "error": null,
                "value": 174
            }
        }
    ]
}

SDK Version

6.39.0

Latest version known to work for scenario above?

No response

Known Workarounds

No response

Debug output

</details>


### Configuration

_No response_

### Other information

_No response_

Bắt đầu trong BatchResponseContent.java tại getResponseFromJsonObject, khoảng dòng 199, và tái hiện phản hồi batch chứa một trường lỗi null rõ ràng. Xác minh rằng giá trị phản hồi vẫn được xử lý thành công và IllegalStateException không còn xảy ra.