**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
}
            returnFromSignature.add(entry.getValue().esType());
        }
        for (int i = 0; i < args.size(); i++) {
            Set<String> annotationTypes = Arrays.stream(args.get(i).type()).collect(Collectors.toCollection(() -> new TreeSet<>()));
            if (annotationTypes.equals(Set.of("?"))) {
                continue; 
            }
            Set<String> signatureTypes = typesFromSignature.get(i);
            if (signatureTypes.isEmpty()) {
                continue;
            }
            assertEquals(annotationTypes, signatureTypes);
        }
        Set<String> returnTypes = Arrays.stream(description.returnType()).collect(Collectors.toCollection(() -> new TreeSet<>()));
        if (returnTypes.equals(Set.of("?")) == false) {
            
            assertEquals(returnTypes, returnFromSignature);
        }
    }
    /**
     * Adds cases with {@code null} and asserts that the result is {@code null}.
     * <p>
     *     Note: This won't add more than a single null to any existing test case,
     *     just to keep the number of test cases from exploding totally.
     * </p>
     * @param  entirelyNullPreservesType should a test case that only contains parameters
     *                                   with the {@code null} type keep it's expected type?
     *                                   This is <strong>mostly</strong> going to be {@code true}
     *                                   except for functions that base their type entirely