ESQL: Unmute and fix BlockMultiValuedTests.testToMask (#124339)

Fixes #124165

Author: ivancea

muted-tests.yml

@@ -336,9 +336,6 @@ tests:
 - class: org.elasticsearch.search.query.QueryPhaseTimeoutTests
   method: testScorerTimeoutTerms
   issue: https://github.com/elastic/elasticsearch/issues/124141
-- class: org.elasticsearch.compute.data.BlockMultiValuedTests
-  method: testToMask {elementType=BOOLEAN nullAllowed=true}
-  issue: https://github.com/elastic/elasticsearch/issues/124165
 - class: org.elasticsearch.smoketest.MlWithSecurityIT
   method: test {yaml=ml/start_data_frame_analytics/Test start classification analysis when the dependent variable is missing}
   issue: https://github.com/elastic/elasticsearch/issues/124168

x-pack/plugin/esql/compute/src/test/java/org/elasticsearch/compute/data/BlockMultiValuedTests.java

@@ -29,6 +29,7 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Objects;
 import java.util.function.IntUnaryOperator;
 import java.util.stream.IntStream;
 
@@ -133,10 +134,12 @@ public void testToMask() {
         if (elementType != ElementType.BOOLEAN) {
             return;
         }
-        int positionCount = randomIntBetween(1, 16 * 1024);
+        int positionCount = randomIntBetween(0, 16 * 1024);
         var b = RandomBlock.randomBlock(blockFactory(), elementType, positionCount, nullAllowed, 2, 10, 0, 0);
         try (ToMask mask = ((BooleanBlock) b.block()).toMask()) {
-            assertThat(mask.hadMultivaluedFields(), equalTo(true));
+            var anyNonNullValue = b.values().stream().anyMatch(Objects::nonNull);
+            assertThat(mask.hadMultivaluedFields(), equalTo(anyNonNullValue));
+
             for (int p = 0; p < b.values().size(); p++) {
                 List<Object> v = b.values().get(p);
                 if (v == null) {