Always true.

Author: mjmbischoff

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/multivalue/MvContainsTests.java

@@ -364,9 +364,9 @@ private static String toSpaceSeparatedString(ArrayList<DataType> typesWithNull)
         return typesWithNull.stream().map(Objects::toString).collect(Collectors.joining(" "));
     }
 
-    // We always return a boolean.
+    // When all arguments are null: the 2nd arg (subset) will be `null` and the 1st is invariant (null,null) => true.
     @Override
     protected Matcher<Object> allNullsMatcher() {
-        return anyOf(equalTo(false), equalTo(true));
+        return equalTo(true);
     }
 }