Fixed the weights null

Author: mridula-s109

x-pack/plugin/rank-rrf/src/main/java/org/elasticsearch/xpack/rank/rrf/RRFRetrieverBuilder.java

@@ -164,13 +164,6 @@ public ActionRequestValidationException validate(
     ) {
         validationException = super.validate(source, validationException, isScroll, allowPartialSearchResults);
 
-        if (this.weights != null) {
-            for (float weight : this.weights) {
-                if (weight < 0) {
-                    validationException = addValidationError("[weight] must be non-negative, found [" + weight + "]", validationException);
-                }
-            }
-        }
         return MultiFieldsInnerRetrieverUtils.validateParams(
             innerRetrievers,
             fields,
@@ -283,11 +276,15 @@ protected RetrieverBuilder doRewrite(QueryRewriteContext ctx) {
                     for (var retriever : r) {
                         retrievers.add(retriever.retrieverSource());
                     }
-                    return new RRFRetrieverBuilder(retrievers, null, null, rankWindowSize, rankConstant, null);
+                    float[] weights = new float[retrievers.size()];
+                    Arrays.fill(weights, 1.0f);
+                    return new RRFRetrieverBuilder(retrievers, null, null, rankWindowSize, rankConstant, weights);
                 },
                 w -> {
-                    if (w < 0) {
-                        throw new IllegalArgumentException("[" + NAME + "] per-field weights must be non-negative");
+                    if (w != 1.0f) {
+                        throw new IllegalArgumentException(
+                            "[" + NAME + "] does not support per-field weights in [" + FIELDS_FIELD.getPreferredName() + "]"
+                        );
                     }
                 }
             );

x-pack/plugin/rank-rrf/src/test/java/org/elasticsearch/xpack/rank/rrf/RRFRetrieverBuilderTests.java

@@ -41,6 +41,7 @@
 import java.util.Set;
 
 import static org.elasticsearch.search.rank.RankBuilder.DEFAULT_RANK_WINDOW_SIZE;
+import static org.elasticsearch.xpack.rank.rrf.RRFRetrieverComponent.DEFAULT_WEIGHT;
 import static org.hamcrest.Matchers.instanceOf;
 
 /** Tests for the rrf retriever. */
@@ -164,7 +165,7 @@ public void testMultiFieldsParamsRewrite() {
             "foo",
             DEFAULT_RANK_WINDOW_SIZE,
             RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
-            null
+            new float[0]
         );
         assertMultiFieldsParamsRewrite(
             rrfRetrieverBuilder,
@@ -181,7 +182,7 @@ public void testMultiFieldsParamsRewrite() {
             "foo2",
             DEFAULT_RANK_WINDOW_SIZE * 2,
             RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT / 2,
-            null
+            new float[0]
         );
         assertMultiFieldsParamsRewrite(
             rrfRetrieverBuilder,
@@ -198,7 +199,7 @@ public void testMultiFieldsParamsRewrite() {
             "bar",
             DEFAULT_RANK_WINDOW_SIZE,
             RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
-            null
+            new float[0]
         );
         assertMultiFieldsParamsRewrite(
             rrfRetrieverBuilder,
@@ -215,7 +216,7 @@ public void testMultiFieldsParamsRewrite() {
             "baz",
             DEFAULT_RANK_WINDOW_SIZE,
             RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
-            null
+            new float[0]
         );
         assertMultiFieldsParamsRewrite(
             rrfRetrieverBuilder,
@@ -247,7 +248,7 @@ public void testSearchRemoteIndex() {
             "foo",
             DEFAULT_RANK_WINDOW_SIZE,
             RRFRetrieverBuilder.DEFAULT_RANK_CONSTANT,
-            null
+            new float[0]
         );
 
         IllegalArgumentException iae = expectThrows(