The test class `KeywordFieldMapperTests` contains a switch statement with a branch that will never execute. The test uses a `between(x, y)` switch expression, but the `4` case is outside the randomised range. We need to fix this before #88739 can be merged. By "fix", I mean either remove the spurious case, or if we actually want it then extend the randomized range.
server/src/test/java/org/elasticsearch/index/mapper/KeywordFieldMapperTests.java
private final String nullValue = usually() ? null : randomAlphaOfLength(2);
        @Override
        public SyntheticSourceExample example(int maxValues) {
            if (randomBoolean()) {
                Tuple<String, String> v = generateValue();
                return new SyntheticSourceExample(v.v1(), v.v2(), this::mapping);
            }
            List<Tuple<String, String>> values = randomList(1, maxValues, this::generateValue);
            List<String> in = values.stream().map(Tuple::v1).toList();
            List<String> outList = values.stream().map(Tuple::v2).collect(Collectors.toSet()).stream().sorted().toList();
            Object out = outList.size() == 1 ? outList.get(0) : outList;
            return new SyntheticSourceExample(in, out, this::mapping);
        }
        private Tuple<String, String> generateValue() {
            if (nullValue != null && randomBoolean()) {
                return Tuple.tuple(null, nullValue);
            }
            String v = randomAlphaOfLength(5);
            return Tuple.tuple(v, v);
        }
        private void mapping(XContentBuilder b) throws IOException {
            b.field("type", "keyword");
            if (nullValue != null) {
                b.field("null_value", nullValue);
            }
        }
        @Override