[BUG] Some complex use cases of `streamstats` failed after "Bump Calcite to 1.41.0"

[ishaoxy]

What is the bug?
The version of Calcite was updated to 1.41.0 in #4714 .
Streamstats command was implemented in #4297 .

These complex use cases worked in the former version of Calcite, but now failed.

  "query": """
  source=stream_test_null | streamstats window=2 avg(age) as avg_age by state, country | streamstats window=2 avg(avg_age) as avg_state_age by country
  """

POST _plugins/_ppl
{
  "query": """
  source=stream_test_null | streamstats reset_before=age>20 avg(age) as avg_age | streamstats reset_before=avg_age>20 window=2 avg(avg_age) as avg_state_age by country
  """
}

POST _plugins/_ppl
{
  "query": """
  source=stream_test_null | streamstats reset_before=age>22 avg(age) as avg_age  | streamstats window=2 avg(avg_age) as avg_state_age by country
  """

It is caused by a NPE. But I still not find the exact reason in the Calcite code.

How can one reproduce the bug?
Steps to reproduce the behavior:

Set data:

POST stream_test_null/_bulk?refresh=true
{"index":{"_id":"1"}}
{"name":"Jake","age":70,"state":"California","country":"USA","year":2023,"month":4}
{"index":{"_id":"2"}}
{"name":"Hello","age":30,"state":"New York","country":"USA","year":2023,"month":4}
{"index":{"_id":"3"}}
{"name":"John","age":25,"state":"Ontario","country":"Canada","year":2023,"month":4}
{"index":{"_id":"4"}}
{"name":"Jane","age":20,"state":"Quebec","country":"Canada","year":2023,"month":4}
{"index":{"_id":"5"}}
{"name":null,"age":10,"state":null,"country":"Canada","year":2023,"month":4}
{"index":{"_id":"6"}}
{"name":"Kevin","year":2023,"month":4}

Then do the query.

What is the expected behavior?
A clear and concise description of what you expected to happen.

What is your host/environment?

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

Do you have any screenshots?

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