update score type (opensearch-project#176)

Author: lucy66hw

CHANGELOG.md

@@ -6,6 +6,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Added
 
 ### Changed
+update `score` type. ([#176](https://github.com/opensearch-project/opensearch-protobufs/pull/176))
 
 ### Removed
 

protos/schemas/search.proto

@@ -452,6 +452,13 @@ message InnerHitsResult {
 
 }
 
+message HitUnderscoreScore {
+  oneof hit_underscore_score {
+    double double = 1;
+    NullValue null_value = 2;
+  }
+}
+
 message HitsMetadataHitsInner {
 
   optional string underscore_type = 1;
@@ -462,7 +469,7 @@ message HitsMetadataHitsInner {
   string underscore_id = 3;
 
   // [optional] Relevance of the returned document.
-  repeated FieldValue score = 4;
+  optional HitUnderscoreScore score = 4;
 
   // [optional] Explanation of how the relevance score (_score) is calculated for every result.
   optional Explanation explanation = 5;