Modify to invoke QueryShardContext.fieldMapper() method to apply allowUnmappedFields and mapUnmappedFieldAsString settings

Signed-off-by: imyp92 <pyw5420@gmail.com>

Author: tokki92

server/src/main/java/org/opensearch/index/query/ExistsQueryBuilder.java

@@ -230,20 +230,16 @@ private static Collection<String> getMappedField(QueryShardContext context, Stri
         if (context.getObjectMapper(fieldPattern) != null) {
             // the _field_names field also indexes objects, so we don't have to
             // do any more work to support exists queries on whole objects
-            fields = Collections.singleton(fieldPattern);
+            return Collections.singleton(fieldPattern);
         } else {
             fields = context.simpleMatchToIndexNames(fieldPattern);
         }
 
         if (fields.size() == 1) {
             String field = fields.iterator().next();
-            MappedFieldType fieldType = context.getMapperService().fieldType(field);
+            MappedFieldType fieldType = context.fieldMapper(field);
             if (fieldType == null) {
-                // The field does not exist as a leaf but could be an object so
-                // check for an object mapper
-                if (context.getObjectMapper(field) == null) {
-                    return Collections.emptySet();
-                }
+                return Collections.emptySet();
             }
         }
 

server/src/main/java/org/opensearch/index/search/QueryParserHelper.java

@@ -143,7 +143,7 @@ static Map<String, Float> resolveMappingField(
                 fieldName = fieldName + fieldSuffix;
             }
 
-            MappedFieldType fieldType = context.getMapperService().fieldType(fieldName);
+            MappedFieldType fieldType = context.fieldMapper(fieldName);
             if (fieldType == null) {
                 continue;
             }