[Bug Report] invoke_endpoint is returning empty list in the response body.

**Link to the notebook**
https://github.com/aws/amazon-sagemaker-examples/blob/main/advanced_functionality/xgboost_bring_your_own_model/xgboost_bring_your_own_model.ipynb

**Describe the bug**
Just ran the code as it is, and found that `runtime_client.invoke_endpoint` always returns an empty list in the response body.

**To reproduce**
Just run all cells of the notebook.

Open advanced_functionality/xgboost_bring_your_own_model/xgboost_bring_your_own_model.ipynb and run all cells to reproduce the empty response from runtime_client.invoke_endpoint. Read the notebook’s endpoint invocation and output-handling cells, then verify that the response body contains the expected prediction list when the notebook completes successfully.

Written by the indexing model from the issue text.