Use optional string for queryText and queryImage.

Signed-off-by: Bo Zhang <[email protected]>

CHANGELOG.md

@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Set neural-search plugin 3.0.0 baseline JDK version to JDK-2 ([#838](https://github.com/opensearch-project/neural-search/pull/838))
 ### Bug Fixes
 - Fix for nested field missing sub embedding field in text embedding processor ([#913](https://github.com/opensearch-project/neural-search/pull/913))
+- Correct NeuralQueryBuilder doEquals() and doHashCode().
 ### Infrastructure
 ### Documentation
 ### Maintenance

src/main/java/org/opensearch/neuralsearch/query/NeuralQueryBuilder.java

@@ -117,8 +117,8 @@ public static void initialize(MLCommonsClientAccessor mlClient) {
     public NeuralQueryBuilder(StreamInput in) throws IOException {
         super(in);
         this.fieldName = in.readString();
-        this.queryText = in.readString();
-        this.queryImage = in.readString();
+        this.queryText = in.readOptionalString();
+        this.queryImage = in.readOptionalString();
         // If cluster version is on or after 2.11 then default model Id support is enabled
         if (isClusterOnOrAfterMinReqVersionForDefaultModelIdSupport()) {
             this.modelId = in.readOptionalString();
@@ -147,8 +147,8 @@ public NeuralQueryBuilder(StreamInput in) throws IOException {
     @Override
     protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeString(this.fieldName);
-        out.writeString(this.queryText);
-        out.writeString(this.queryImage);
+        out.writeOptionalString(this.queryText);
+        out.writeOptionalString(this.queryImage);
         // If cluster version is on or after 2.11 then default model Id support is enabled
         if (isClusterOnOrAfterMinReqVersionForDefaultModelIdSupport()) {
             out.writeOptionalString(this.modelId);