[BUG] Generating embeddings for arrays of objects is broken starting 2.17

[Zhangxunmt]

What is the bug? Following this tutorial https://opensearch.org/docs/2.17/ml-commons-plugin/tutorials/generate-embeddings/, you will get the results like below. The title_embedding is not correctly ingested into the books as the new field. This results do not match what's in the tutorial.

{
  "docs": [
    {
      "doc": {
        "_index": "my_books",
        "_id": "1",
        "_source": {
          "_ingest": {
            "_value": {
              "title_embedding": [
                0.009794682,
                0.04060341,
                0.016146386,
                ...
                -0.03778624
              ]
            }
          },
          "books": [
            {
              "title": "first book",
              "description": "This is first book"
            },
            {
              "title": "second book",
              "description": "This is second book"
            }
          ]
        },
        "_ingest": {
          "_value": null,
          "timestamp": "2025-03-14T22:02:43.240620757Z"
        }
      }
    }
  ]
}

How can one reproduce the bug? Follow the tutorial, and you will duplicate the error.

What is the expected behavior? The results in the tutorial is expected - new embeddings are ingested into the Books.

What is your host/environment?

• OS: [e.g. iOS]
• Version [e.g. 22]
• Plugins

Do you have any screenshots? If applicable, add screenshots to help explain your problem.

Do you have any additional context? Add any other context about the problem.