[BUG] Null functions with struct field

[currantw]

What is the bug?

The functions isnull and isnotnull appear to throw an exception when applied to an object/struct field.

How can one reproduce the bug?

Input data:

root
{ "a": "x", "b": 0 }
{ "a": null, "b": 1 }
{ "a": "y", "b": null }
null

source=data | where isnull(root)
source=data | where isnotnull(root)

Exception:

{
  "error": {
    "reason": "Error occurred in OpenSearch engine: all shards failed",
    "details": "Shard[0]: java.lang.IllegalArgumentException: No field found for [root] in mapping\n\nFor more details, please send request for Json format to see the raw response from OpenSearch engine.",
    "type": "SearchPhaseExecutionException"
  },
  "status": 400
}

What is the expected behaviour?

Expected:

root
{ "a": "x", "b": 0 }
{ "a": null, "b": 1 }
{ "a": "y", "b": null }

What is your host/environment?

• OS: iOS
• Plugins: PPL

Do you have any screenshots?

Do you have any additional context?

None.