Add NOOP IgnoredFieldsLoader

Author: jordan-powers

server/src/main/java/org/elasticsearch/index/mapper/IgnoredSourceFieldMapper.java

@@ -269,6 +269,16 @@ public static Set<String> ensureLoaded(Set<String> fieldsToLoadForSyntheticSourc
     }
 
     public enum IgnoredFieldsLoader {
+        NO_IGNORED_SOURCE {
+            @Override
+            public Map<String, List<IgnoredSourceFieldMapper.NameValue>> loadIgnoredFields(
+                SourceFilter filter,
+                LeafStoredFieldLoader storedFieldLoader,
+                Map<String, SourceLoader.SyntheticFieldLoader.StoredFieldLoader> storedFieldLoaders
+            ) {
+                return Map.of();
+            }
+        },
         SINGLE_IGNORED_SOURCE {
             @Override
             public Map<String, List<IgnoredSourceFieldMapper.NameValue>> loadIgnoredFields(

server/src/main/java/org/elasticsearch/index/mapper/Mapping.java

@@ -155,7 +155,7 @@ public SourceLoader.SyntheticFieldLoader syntheticFieldLoader(@Nullable SourceFi
     public IgnoredSourceFieldMapper.IgnoredFieldsLoader ignoredFieldsLoader() {
         IgnoredSourceFieldMapper isfm = (IgnoredSourceFieldMapper) metadataMappersByName.get(IgnoredSourceFieldMapper.NAME);
         if (isfm == null) {
-            return null;
+            return IgnoredSourceFieldMapper.IgnoredFieldsLoader.NO_IGNORED_SOURCE;
         }
         return isfm.ignoredFieldsLoader();
     }