**Build scan:**
https://gradle-enterprise.elastic.co/s/fvg2knbi424p4/tests/:x-pack:plugin:esql:test/org.elasticsearch.xpack.esql.expression.function.scalar.conditional.LeastTests/testEvaluateInManyThreads%20%7BTestCase=(%3Ckeyword%3E,%20%3Ckeyword%3E,%20%3Ckeyword%3E,%20%3Ckeyword%3E,%20%3Ckeyword%3E,%20%3Ckeyword%3E,%20%3Ckeyword%3E)%20null%20in%204%7D
**Reproduction lines:**
```
gradlew ':x-pack:plugin:esql:test' --tests "org.elasticsearch.xpack.esql.expression.function.scalar.conditional.GreatestTests.testEvaluateInManyThreads {TestCase=(<mv_integer>) null in 0}" -Dtests.seed=BCCD8A2AFCEA37CB -Dtests.locale=zh -Dtests.timezone=Europe/Guernsey -Druntime.java=21

gradlew ':x-pack:plugin:esql:test' --tests "org.elasticsearch.xpack.esql.expression.function.scalar.conditional.LeastTests.testEvaluateInManyThreads {TestCase=(<keyword>, <keyword>, <keyword>, <keyword>, <keyword>, <keyword>, <keyword>) null in 4}" -Dtests.seed=BCCD8A2AFCEA37CB -Dtests.locale=lt -Dtests.timezone=Indian/Christmas -Druntime.java=21

 gradlew ':x-pack:plugin:esql:test' --tests "org.elasticsearch.xpack.esql.expression.function.scalar.conditional.GreatestTests.testEvaluateInManyThreads {TestCase=(<mv_integer>) null in 0}" -Dtests.seed=BCCD8A2AFCEA37CB -Dtests.locale=zh -Dtests.timezone=Europe/Guernsey -Druntime.java=21
```

**Applicable branches:**
main

**Reproduces locally?:**
Yes

**Failure history:**
https://gradle-enterprise.elastic.co/scans/tests?tests.container=org.elasticsearch.xpack.esql.expression.function.scalar.conditional.LeastTests&tests.test=testEvaluateInManyThreads%20%7BTestCase%3D(%3Ckeyword%3E,%20%3Ckeyword%3E,%20%3Ckeyword%3E,%20%3Ckeyword%3E,%20%3Ckeyword%3E,%20%3Ckeyword%3E,%20%3Ckeyword%3E)%20null%20in%204%7D


**Failure excerpt:**
```
org.elasticsearch.xpack.esql.expression.function.scalar.conditional.GreatestTests > classMethod FAILED
    java.lang.AssertionError: expected:<[boolean, double, integer, ip, keyword, long, text, version]> but was:<[integer]>


```
x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/AbstractFunctionTestCase.java
either(sameInstance(context.blockFactory())).or(sameInstance(inputBlockFactory))
                );
            }
        } finally {
            Releasables.close(onePositionPage::releaseBlocks, Releasables.wrap(manyPositionsBlocks));
        }
        if (testCase.getExpectedWarnings() != null) {
            assertWarnings(testCase.getExpectedWarnings());
        }
    }
    
    public final void testSimpleWithNulls() { 
        assumeTrue("nothing to do if a type error", testCase.getExpectedTypeError() == null);
        assumeTrue("All test data types must be representable in order to build fields", testCase.allTypesAreRepresentable());
        List<Object> simpleData = testCase.getDataValues();
        try (EvalOperator.ExpressionEvaluator eval = evaluator(buildFieldExpression(testCase)).get(driverContext())) {
            Block[] orig = BlockUtils.fromListRow(BlockFactory.getNonBreakingInstance(), simpleData);
            for (int i = 0; i < orig.length; i++) {
                List<Object> data = new ArrayList<>();
                Block[] blocks = new Block[orig.length];
                for (int b = 0; b < blocks.length; b++) {
                    if (b == i) {
                        blocks[b] = orig[b].elementType().newBlockBuilder(1).appendNull().build();
                        data.add(null);
                    } else {
                        blocks[b] = orig[b];
                        data.add(simpleData.get(b));
                    }
                }
                try (Block.Ref ref = eval.eval(new Page(blocks))) {