Always write doc_values param to mapping for wildcard field (#16988)

Author: msfroh

server/src/main/java/org/opensearch/index/mapper/WildcardFieldMapper.java

@@ -102,7 +102,7 @@ public static final class Builder extends ParametrizedFieldMapper.Builder {
         );
         private final Parameter<String> normalizer = Parameter.stringParam("normalizer", false, m -> toType(m).normalizerName, "default");
         private final Parameter<Map<String, String>> meta = Parameter.metaParam();
-        private final Parameter<Boolean> hasDocValues = Parameter.docValuesParam(m -> toType(m).hasDocValues, false);
+        private final Parameter<Boolean> hasDocValues = Parameter.docValuesParam(m -> toType(m).hasDocValues, false).alwaysSerialize();
         private final IndexAnalyzers indexAnalyzers;
 
         public Builder(String name, IndexAnalyzers indexAnalyzers) {

server/src/test/java/org/opensearch/index/mapper/WildcardFieldMapperTests.java

@@ -49,6 +49,7 @@ public class WildcardFieldMapperTests extends MapperTestCase {
     @Override
     protected void minimalMapping(XContentBuilder b) throws IOException {
         b.field("type", "wildcard");
+        b.field("doc_values", false);
     }
 
     @Override
@@ -59,7 +60,10 @@ protected void writeFieldValue(XContentBuilder builder) throws IOException {
     @Override
     protected void registerParameters(ParameterChecker checker) throws IOException {
         checker.registerConflictCheck("normalizer", b -> b.field("normalizer", "lowercase"));
-        checker.registerConflictCheck("doc_values", b -> b.field("doc_values", true));
+        checker.registerConflictCheck("doc_values", fieldMapping(this::minimalMapping), fieldMapping(xcb -> {
+            xcb.field("type", "wildcard");
+            xcb.field("doc_values", true);
+        }));
         checker.registerConflictCheck("null_value", b -> b.field("null_value", "foo"));
         checker.registerUpdateCheck(b -> b.field("ignore_above", 256), m -> assertEquals(256, ((WildcardFieldMapper) m).ignoreAbove()));
     }