**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
if (nullPositions.size() == positions) {
            nullPositions = Set.of();
        }
        try {
            for (int b = 0; b < data.size(); b++) {
                ElementType elementType = LocalExecutionPlanner.toElementType(data.get(b).type());
                try (Block.Builder builder = elementType.newBlockBuilder(positions, inputBlockFactory)) {
                    for (int p = 0; p < positions; p++) {
                        if (nullPositions.contains(p)) {
                            builder.appendNull();
                        } else {
                            builder.copyFrom(onePositionPage.getBlock(b), 0, 1);
                        }
                    }
                    manyPositionsBlocks[b] = builder.build();
                }
            }
            Expression expression = readFloating ? buildDeepCopyOfFieldExpression(testCase) : buildFieldExpression(testCase);
            try (ExpressionEvaluator eval = evaluator(expression).get(context); Block.Ref ref = eval.eval(new Page(manyPositionsBlocks))) {
                assertThat(ref.block().getPositionCount(), equalTo(ref.block().getPositionCount()));
                for (int p = 0; p < positions; p++) {
                    if (nullPositions.contains(p)) {
                        assertThat(toJavaObject(ref.block(), p), allNullsMatcher());
                        continue;
                    }
                    assertThat(toJavaObject(ref.block(), p), testCase.getMatcher());
                }
                assertThat(
                    "evaluates to tracked block",
                    ref.block().blockFactory(),