[BUG] percentile returns wrong value in V2

[xinyual]

What is the bug?
When we use percentile aggregation but no input, it will return 0 instead of null.

How can one reproduce the bug?
Create a index with two items

POST /demo/_doc
{
    "demo1": 1,
    "demo2": 1
}

POST /demo/_doc
{
    "demo1": null,
    "demo2": null
}

Then call calcite

POST /_plugins/_ppl/
{
    "query": "source=demo | stats percentile(demo1, 50) by demo2"
}

It returns

{
    "schema": [
        {
            "name": "percentile(demo1, 50)",
            "type": "long"
        },
        {
            "name": "demo2",
            "type": "long"
        }
    ],
    "datarows": [
        [
            0,
            null
        ],
        [
            1,
            1
        ]
    ],
    "total": 2,
    "size": 2
}

Here we return 0 for the bin when demo2 is null. But actually no any input here. So we should return null. 0 has quantitative meanings .

What is the expected behavior?
Return null

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.

[LantaoJin]

Thanks, this was fixed in v3. linked to #3487