ESQL: Unmute nullify tests with STATS

[alex-spies]

Relates #138888 and #139797

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[idegtiarenko]

Why it become double? Looks like x in row could be cast to int or long

[ivancea]

Note that foo doesn't exist; x is unused.
About why double, I suspect it's a purely technical thing related with this condition:

elasticsearch/x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/aggregate/Sum.java

Lines 120 to 124 in f50da31

	@Override
	public DataType dataType() {
	DataType dt = field().dataType();
	return dt.isWholeNumber() == false || dt == UNSIGNED_LONG ? DOUBLE : LONG;
	}

dt.isWholeNumber() == false -> double. Alex may confirm what is the field type here. If it's NULL, and as NULL isn't a whole number, double it is!

[alex-spies]

Excellent question @idegtiarenko .

Ivan's answer is correct, although that boils down to "because we said so" when we implemented SUM.

I'll sleep better after double checking this, but currently this is consistent with ROW x = null | STATS SUM(x).

For sleeping better, I opened #140577.

[elasticsearchmachine]

💔 Backport failed

Status	Branch	Result
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[alex-spies]

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