**Build scan:**
https://gradle-enterprise.elastic.co/s/eafsb3toi26t6/tests/:x-pack:plugin:core:test/org.elasticsearch.xpack.core.ml.inference.trainedmodel.QuestionAnsweringConfigUpdateTests/testApply

**Reproduction line:**
`./gradlew ':x-pack:plugin:core:test' --tests "org.elasticsearch.xpack.core.ml.inference.trainedmodel.QuestionAnsweringConfigUpdateTests.testApply" -Dtests.seed=B72F5E39AAA25004 -Dtests.locale=et -Dtests.timezone=America/Merida -Druntime.java=17`

**Applicable branches:**
master

**Reproduces locally?:**
Yes

**Failure history:**
https://gradle-enterprise.elastic.co/scans/tests?tests.container=org.elasticsearch.xpack.core.ml.inference.trainedmodel.QuestionAnsweringConfigUpdateTests&tests.test=testApply

**Failure excerpt:**
```
org.elasticsearch.ElasticsearchStatusException: [num_top_classes] must be greater than or equal to [0]; provided [-1]

  at __randomizedtesting.SeedInfo.seed([B72F5E39AAA25004:9B90E7660074634D]:0)
  at org.elasticsearch.xpack.core.ml.utils.ExceptionsHelper.badRequestException(ExceptionsHelper.java:89)
  at org.elasticsearch.xpack.core.ml.inference.trainedmodel.QuestionAnsweringConfig.<init>(QuestionAnsweringConfig.java:93)
  at org.elasticsearch.xpack.core.ml.inference.trainedmodel.QuestionAnsweringConfigUpdateTests.testApply(QuestionAnsweringConfigUpdateTests.java:115)
  at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java:-2)
  at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
  at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:568)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.invoke(RandomizedRunner.java:1758)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$8.evaluate(RandomizedRunner.java:946)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$9.evaluate(RandomizedRunner.java:982)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$10.evaluate(RandomizedRunner.java:996)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleSetupTeardownChained$1.evaluate(TestRuleSetupTeardownChained.java:44)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at org.apache.lucene.tests.util.TestRuleThreadAndTestName$1.evaluate(TestRuleThreadAndTestName.java:45)
  at org.apache.lucene.tests.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:60)
  at org.apache.lucene.tests.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:44)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:375)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl.forkTimeoutingTask(ThreadLeakControl.java:824)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$3.evaluate(ThreadLeakControl.java:475)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.runSingleTest(RandomizedRunner.java:955)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$5.evaluate(RandomizedRunner.java:840)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$6.evaluate(RandomizedRunner.java:891)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$7.evaluate(RandomizedRunner.java:902)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleStoreClassName$1.evaluate(TestRuleStoreClassName.java:38)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleAssertionsRequired$1.evaluate(TestRuleAssertionsRequired.java:53)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at org.apache.lucene.tests.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:44)
  at org.apache.lucene.tests.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:60)
  at org.apache.lucene.tests.util.TestRuleIgnoreTestSuites$1.evaluate(TestRuleIgnoreTestSuites.java:47)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:375)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl.lambda$forkTimeoutingTask$0(ThreadLeakControl.java:831)
  at java.lang.Thread.run(Thread.java:833)

```
x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ml/inference/trainedmodel/QuestionAnsweringConfigUpdateTests.java
public static QuestionAnsweringConfigUpdate randomUpdate() {
        return new QuestionAnsweringConfigUpdate(
            randomAlphaOfLength(10),
            randomBoolean() ? null : randomIntBetween(0, 15),
            randomBoolean() ? null : randomIntBetween(1, 100),
            randomBoolean() ? null : randomAlphaOfLength(5),
            randomBoolean() ? null : new BertTokenizationUpdate(randomFrom(Tokenization.Truncate.values()), null)
        );
    }
    public static QuestionAnsweringConfigUpdate mutateForVersion(QuestionAnsweringConfigUpdate instance, Version version) {
        if (version.before(Version.V_8_1_0)) {
            return new QuestionAnsweringConfigUpdate(
                instance.getQuestion(),
                instance.getNumTopClasses(),
                instance.getMaxAnswerLength(),
                instance.getResultsField(),
                null
            );
        }
        return instance;
    }
    @Override
    protected boolean supportsUnknownFields() {