Avoid merging raw query params if there is no custom raw query params

Author: zoewangg

core/sdk-core/src/main/java/software/amazon/awssdk/core/internal/http/pipeline/stages/MergeCustomQueryParamsStage.java

@@ -33,6 +33,10 @@ public class MergeCustomQueryParamsStage implements MutableRequestToRequestPipel
     @Override
     public SdkHttpFullRequest.Builder execute(SdkHttpFullRequest.Builder request, RequestExecutionContext context)
             throws Exception {
+        if (context.requestConfig().rawQueryParameters().isEmpty()) {
+            return request;
+        }
+
         return request.rawQueryParameters(mergeParams(request, context));
     }