fix unsuported operation (#4733)

Signed-off-by: Hailong Cui <ihailong@amazon.com>

Author: Hailong-am

common/src/main/java/org/opensearch/ml/common/indexInsight/AbstractIndexInsightTask.java

@@ -15,7 +15,6 @@
 
 import java.nio.charset.StandardCharsets;
 import java.time.Instant;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -471,11 +470,14 @@ protected static void callLLMWithAgent(
         String sourceIndex,
         ActionListener<String> listener
     ) {
+        Map<String, String> params = new HashMap<>();
+        params.put("prompt", prompt);
+
         AgentMLInput agentInput = AgentMLInput
             .AgentMLInputBuilder()
             .agentId(agentId)
             .functionName(FunctionName.AGENT)
-            .inputDataset(RemoteInferenceInputDataSet.builder().parameters(Collections.singletonMap("prompt", prompt)).build())
+            .inputDataset(RemoteInferenceInputDataSet.builder().parameters(params).build())
             .build();
 
         MLExecuteTaskRequest executeRequest = new MLExecuteTaskRequest(FunctionName.AGENT, agentInput);